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The actions exerted by yawed wind on the crossarm substantially differ from those on the tower body due to the presence of the angle between the crossarm's cross-section and the incoming flow, and this phenomenon deserves a better understanding. Focusing on the tubular crossarms with round-section members, this paper aims to determine insights into wind actions, as affected by various factors, such as the tower type, the mean width to mean height ratio, the solidity ratio, and the wind incidence angle, and thereby derive the wind loads for design. Accordingly, a succession of wind tunnel tests was conducted by using quadrilateral and triangular crossarm models with various solidity ratios and mean width to mean height ratios. The method of direct force measurement (DFM) is employed for the high frequency force balance (HFFB) test to attain the transverse and longitudinal forces on the crossarm simultaneously. It was found that the wind load coefficients increase with increases of the mean width to mean height ratio and decreases of the solidity ratio. Moreover, in the case of the incoming flow perpendicular to the crossarm face, it is concluded that compared to the quadrilateral crossarm, the triangular crossarm possesses a relatively smaller drag coefficient, provided a moderate mean width to mean height ratio of 1.19. Furthermore, an analysis of the experimental results shows that the skewed wind load factor specified in the relevant codes would overestimate the effects of the wind incidence angle and the variations in mean width to mean height ratio, which is evident in the tests but not considered in the codes. It is worth noting that the experimental results show that the crosswind force is pronounced, which is usually ignored in the skewed wind load factor-based approach. Comparatively, using wind load distribution factors seems to be more rational. Thus, the corresponding estimating equations are proposed for the wind load-distribution factors of the crossarms, which agree well with the experimental results. The developed equations would greatly facilitate the determination of wind loads on tubular crossarms. [ABSTRACT FROM AUTHOR]

This paper presents a procedure for rehabilitating plastic hinges with damaged/fractured weldable longitudinal rebars in severely damaged reinforced concrete (RC) bridge columns and possible improvements regarding connection protection and plastic hinge development. Damaged/fractured longitudinal rebars are replaced with new rebar segments, and the basis of this approach involves connecting intermediate machined parts to the original longitudinal rebars by welding with an off-the-shelf steel equal angle. The proposed rehabilitation design procedure is based on capacity design principles, with equations that define the new geometries and required ductility, and it is validated experimentally on three 1∶6 -scale RC circular column specimens. Compared with the original columns, the ductility capacity of the rehabilitated columns increased from 39% to 58%, and the energy dissipation (equivalent viscous damping ratio) increased from approximately 50% to 250%. The base shears of the rehabilitated columns were smaller than those of the original columns owing to the reduction in the rebar area; thus, shear failure was avoided, and the demand on the foundation was reduced. The rehabilitation procedure, by adopting a welding connection that is easily performed on site and concentrates the damage in the new rebar segments, promises to be a quick, simple, reliable, and effective means to improve the ductility and shear capacity of RC bridge columns without using mechanical couplers or changing the column dimensions. [ABSTRACT FROM AUTHOR]

Reliable reduction factors for timber mechanical properties at elevated temperatures are needed to design timber structures for fire safety as well as to assess the safety of historic timber structures against fire hazards. In this paper, a compilation of the available data on the compressive and tensile strengths of timber at elevated temperatures is carried out. Then, a probabilistic modeling approach to predict the temperature-dependent reduction factors applicable to fire design is proposed. The collected data cover both solid and engineered timber at temperatures from 20°C to 300°C, with a variety of sample sizes, wood species, test protocols, and moisture content used in the experiments. The data revealed a large scatter in elevated temperature strengths, and a large conservativeness of the relationships of the current European standard, which is commonly used for the advanced design of timber structures under fire. To address this variability, multiple probability density functions were calibrated across the temperature range, quantifying the goodness of fit with statistical criteria. Two-parameter Weibull functions provided the best fit, and continuous temperature-dependent relationships were derived for the parameters of the distribution. The proposed probabilistic models can be implemented in a numerical code, facilitating their use in analytical and computational approaches, and can be applied to the probabilistic assessment of the structural performance and reliability of timber structures against fire. [ABSTRACT FROM AUTHOR]

This paper presents a testing and numerical modeling program on the global stability and resistance of stainless steel hot-rolled channel section beam–columns under combined compression and minor-axis bending. The testing program comprised material tests, imperfection measurements, and 18 beam–column tests. Following the testing program, systematic numerical simulations were conducted; finite-element models were developed to simulate the test observations and conduct parametric studies to obtain more numerical data. The obtained experimental and numerical results were analyzed and used to perform a design analysis, in which the accuracy of interaction curves prescribed in the US and European design codes for stainless steel hot-rolled channel section beam–columns was assessed comprehensively. The results of the design analysis generally revealed that both the US and European interaction curves yield unduly inaccurate and scattered resistance predictions due to the use of inappropriate curve shape and inaccurate end points. A new design interaction formula is proposed using a more appropriate curve shape and more-accurate end points. The new interaction curve was shown to be capable of offering greatly improved design accuracy and consistency compared with the US and European curves. [ABSTRACT FROM AUTHOR]

In order to avoid the occurrence of serious casualties and secondary injuries caused by high-speed splashing concrete fragments, pendulum impact test research and numerical analysis were carried out for the first time on the civil air defense wall sprayed with 2-mm polyisocyanate-oxazodone (POZD) coatings at different positions. The results showed that spraying a 2-mm POZD coating on the civil air defense wall can significantly reduce the damage area of the wall, restrain the splashing of concrete fragments, ensure the integrity of the wall, and improve the impact resistance and airtightness of the civil air defense wall. The large-rupture-strain fiber-reinforced polymer (FRP) pasted on the back significantly improved the bending stiffness and deformation capacity and reduced the residual displacement of the wall. The failure modes and failure characteristics of the wall obtained through the experiments in this paper provide the failure evaluation criteria for existing civil air defense walls. [ABSTRACT FROM AUTHOR]

This paper presents a proposed design methodology which combines the fire beam element (FBE) for skeletal frame analysis with the slab panel method (SPM) for floor experiencing catenary action. The methodology enables the two systems to interact with each other to provide a simplistic manner to design a full composite structure. The design methodology consists of an iterative process in which (1) the SPM is used to design the composite slab and provides the loads on the support beams of the skeletal structure, and then (2) the FBE analysis, implemented in OpenSees version 2.5.0, determines the deflection of the edge support beams which are used to update the SPM calculations. The existing two-dimensional (2D) FBE finite-element matrices are updated for a three-dimensional FBE, while the SPM is modified to allowing the interaction between the FBE analysis and the SPM. Three validation studies of the FBE analysis show that the FBE analysis is able to capture the behavior of the skeletal structure adequately, as long as the support edge beams of the slab panel have sufficient strength to support the slab panel. The application of the design methodology to an office building serves as a proof on concept and demonstrates that the deflection of the edge beams does have a significant impact on the predicted ultimate load-carrying capacity of the slab panel. [ABSTRACT FROM AUTHOR]

Modal frequencies are widely used to capture dynamics and reveal possible failures of bridge structures. However, the non-Gaussianity and nonlinearity of nonstationary modal frequencies associated with the actual structure under changing environmental conditions often restrict the application in structural health monitoring. Therefore, a new localized frequency cointegration without environmental measurements for the elimination of environmental interference and damage warning is proposed in this paper. The k -nearest neighbor rule is first employed to search for sufficient nearest neighbors for each modal feature based on similarity measurements over a wide range of training data. After that, the cointegration analysis associated with the Johansen procedure is performed to remove environmental trends and obtain multivariable cointegration residuals. Then, the defined early warning index (i.e., the weighted Mahalanobis distance) derived from the exponentially weighted moving average is adopted with respect to the identification of subtle damage. Eight groups of cointegration models between nonstationary modal variables are constructed and validated on the Z24 bridge case. The results demonstrate that the proposed approach can successfully discard spurious influences of environmental variations and identify the occurrence of real structural damage compared to traditional methods. Additionally, this approach is not constrained by the statistical distribution of observation samples, and the selection and combination of different modal orders are crucial in capturing the changes in frequency anomalies for the bridge condition assessment. [ABSTRACT FROM AUTHOR]

The reduced damage and residual deformations of rocking systems make them efficient for designing resilient buildings for earthquakes. This paper presents a design approach for multiple-rocking coupled self-centering concentrically braced frames (SC-CBFs) with linear fluid viscous dampers (FVDs) utilizing an efficient gradient-based optimization procedure. The optimization problem is formulated such that the framing system, the post-tensioning layout, and the location of the rocking sections are simultaneously designed with the FVDs. The constraints of the optimization problem are formulated following performance-based seismic design. These constraints are evaluated based on results obtained from nonlinear time history analyses of the system when subjected to an ensemble of ground motion records. For the first time, a design method suitable for irregular buildings with multiple-rocking coupled SC-CBFs is proposed. A nine-story irregular building was designed using the proposed method. The results show that an efficient design can be achieved with reasonable computational effort. In addition, the results show that the design of these buildings is not intuitive. A multiple-rocking solution was obtained to reduce force demands in the framing elements. [ABSTRACT FROM AUTHOR]

The slotted-hidden-gap (SHG) connection eliminates the need to reinforce the slot region of hollow structural sections (HSS) braces of concentrically braced frames (CBFs). However, the existing design approach for SHG connections is rather empirical and limited by the range of the connection geometries and materials that had previously been tested. A general design approach based on the findings of a large-scale parametric study is presented in this paper, where the most critical parameters of the connection were varied. Different weld configurations were investigated to examine the effect of shear lag on the overall performance of the brace. The inelastic performance of SHG-connected braces designed using the proposed approach was validated by means of numerically simulating the resulting braces and connections and subjecting them to a reversed-cyclic loading protocol. The simulated braces were able to attain their yield tensile resistance and fracture away from the connection region while sustaining an axial deformation corresponding to an average story drift of 5.43%. The proposed design and detailing method was, as such, found to be effective in the design of square HSS SHG connection braces ranging in size and steel grade. [ABSTRACT FROM AUTHOR]

The seismic qualification and seismic performance assessment of suspended ceiling systems have been traditionally conducted through large-scale shake table testing. This experimentally-based approach not only involves significant financial and time resources but is also not flexible to evaluate several configurations of suspended ceiling systems. As an alternate approach, this paper discusses the development of a general finite-element (FE) model of suspended ceiling systems that accurately captures the propagation of damage observed during full-scale shake table testing using the commercial finite-element analysis software, Abaqus/Explicit. The results of the large-scale shake table testing on suspended ceiling systems conducted at the University at Buffalo as part of the NEES nonstructural project were used to validate the FE model. The major components of suspended ceiling systems such as grid runners, ceiling tiles, and hanger wires were modeled and assembled with significant detail in the FE model. The properties of the connections between the grid runners, which are vital for capturing the seismic behavior of suspended ceiling systems were derived numerically. A user-defined subroutine was incorporated in the Abaqus/Explicit software framework to capture the multidirectional pinched hysteretic behavior of the connections between grid runners. An illustrative example of the application of the proposed FE model to develop robust numerically generated fragility curves for suspended ceiling systems is presented. [ABSTRACT FROM AUTHOR]

Steel bar corrosion is one of the most common causes of structural performance degradation for reinforced concrete (RC) columns subjected to extreme loads such as earthquakes. Due to the different characteristics of corrosion effects, a comprehensive and efficient finite element (FE) modeling approach is necessary for the performance assessment of corroded RC columns. To this end, this study provides an effective FE modeling approach using a recently developed geometrically nonlinear fiber-based frame element that considers bond-slip, allowing for explicit representation of corrosion-affected bonding. This aspect necessitates the use of an explicit material model for corroded bond-slip and its associated corroded properties. Since the existing models of corroded bonding properties in the literature were developed based on the highly scattered and limited experimental data, this study develops a new probabilistic model for corroded bonding properties based on more experimental data compiled from the literature and quantifies the prevailing uncertainties. To facilitate its use for modeling corroded RC structures, a cyclic corroded bond-slip model in an open-source FE software framework is implemented. In this paper, the FE modeling approach is first used to model two corroded RC columns tested in the literature, with comparison to the conventional modeling approach (i.e., assuming perfect bonding). The influence of corroded bonding on the static and dynamic behaviors of RC columns is further explored deterministically. Furthermore, the impact of uncertainty in corroded bonding properties on the static and dynamic behavior simulations of RC columns is examined. This work is concluded that (1) the FE modeling approach provided for corroded RC columns proves to be effective in capturing corrosion effects; and (2) corroded bonding plays an important role in simulating the behavior of corroded RC columns, and thus cannot be neglected. This is particularly true considering its associated uncertainty and its impact on the performance assessment of RC columns under severe corrosion conditions. [ABSTRACT FROM AUTHOR]

Since the events of September 11, 2001, the engineering community has devoted increased attention to evaluating the vulnerability of multistory buildings to disproportionate collapse, including substantial research and standards development. This paper reviews recent research conducted by the NIST on the robustness of RC buildings, including experimental validation of both high-fidelity and reduced-order modeling approaches using measurements from subsystems and an entire building tested under column removal scenarios. A robustness index was developed using pushdown analysis of a structure with initial damage to allow an evaluation and comparison of the disproportionate collapse potential of various structural systems using the validated modeling approaches. It is shown that the robustness index is sensitive to differences in the strength and detailing of the structural system, providing higher values for buildings with more stringent design requirements. Further, the paper presents a novel approach for enhancing the robustness of RC beams through local debonding of tensile reinforcing bars at the joints, where significant cracking occurs after a column loss. Experimental and computational studies were conducted to demonstrate the efficacy of this approach. It is shown that debonding of the bottom bars for a length of two beam depths on each side of a central column results in an improvement of more than 30% in the peak vertical load-carrying capacity under a column removal scenario. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental and numerical investigation to obtain a simplified analytical method to calculate intumescent coating thermal conductivity and temperatures of intumescent coating–protected concrete-filled circular steel tubular sections by using an equivalent section factor for the steel section without concrete infill. An important test of correctness of the equivalent steel section factor is that when the resulting thermal conductivity of the intumescent coatings is used in numerical modeling of concrete-filled sections, the steel and concrete core temperatures can be accurately calculated. This paper first reports the experimental results of 32 fire tests conducted on intumescent coating–protected concrete-filled circular sections; experimental variables included coating thickness and circular section dimensions. The fire test results are then used to assess the the accuracy of two existing methods of calculating the equivalent steel section factor. These methods were shown to give a wide range of effective thermal conductivity–temperature relationships for the same intumescent coating and not being able to accurately predict the steel and concrete core temperatures consistently. This paper then proposes a new equation to calculate the equivalent steel section factor, which is demonstrated to be able to more accurately predict the temperatures of intumescent coating–protected concrete-filled steel sections. [ABSTRACT FROM AUTHOR]

The lateral strength and stiffness requirements due to wind loads usually govern the design of tall buildings. The current building codes in the US, Canada, and Europe recognize the first significant yield point as an ultimate limit state. Consequently, the current design practices ignore the plastic capacity of structural systems in the nonlinear range, which could result in overdesigned buildings. Thus, the classical linear-elastic design arguments shall be reexamined with consideration of performance-based wind design (PBWD) approaches, innovative technologies, and materials. We are presenting two companion papers to demonstrate the benefits of considering the nonlinear capacity of structural systems in the design of wind-excited buildings. In this paper, Part I, we have postulated and then proved the capability of self-centering systems in controlling the possible damage accumulation in structural systems subjected to along-wind loads. Our arguments are based on an extensive parametric study through nonlinear time history analyses considering peak and residual ductility-demands, normalized hysteretic energy dissipation, and the rate of damage accumulation as performance indicators. Overall, the results of the parametric study revealed that self-centering systems could benefit the most from the ductility-based design due to their inherent recentering capability, higher energy dissipation, and lower sensitivity to wind duration. Consistent with the notion of PBWD, for self-centering systems, the companion Part II paper demonstrates the benefits of the ductility-based wind design in terms of economics and safety through structural reliability analysis. [ABSTRACT FROM AUTHOR]

Part I of the two companion papers postulated and proved the capability of self-centering systems in controlling the wind-induced damage accumulations due to long-duration along-wind loads. The present Part II paper demonstrates the benefits of ductility-based wind design in terms of economics and safety through structural reliability analysis. Initially, for self-centering systems, the ductility demands are estimated for various levels of force reduction factors, structural damping, postyield stiffness ratio, natural frequency, and energy dissipation capacity. To reduce the computational cost of structural reliability analysis, empirical equations of the mean of peak ductility demands are derived in terms of the force reduction factor and natural frequency. In the reliability estimations, two limit states, the first significant yield and incipient collapse, are considered. Both analytical and simulation techniques are used to compute the failure probabilities by considering uncertainties in both the wind load effects and capacity. Overall, the results indicate that ductile self-centering systems could be designed for reduced along-wind loads and still achieve the minimum required safety level. The results also reveal that self-centering systems designed using the linear-elastic approach but additionally detailed for ductility have a significant reserve of safety against incipient collapse. [ABSTRACT FROM AUTHOR]

To satisfy the easy-repair demands of precast concrete (PC) frames after an earthquake, a PC frame with replaceable artificial controllable plastic hinges (ACPHs) is proposed in this paper. ACPHs were installed at each beam end on both sides of the frame, which concentrated the structural deformation to avoid any damage of precast reinforced concrete members. In this study, to explore the seismic behavior and ACPH location factor on the seismic performance of the frame structures, cyclic loading tests were conducted on two precast concrete frames with different positionings of the ACPH and cast-in-situ frame. The test results indicate that the ACPH frame exhibited favorable seismic performance, and the bearing capacity and energy dissipation capacity can be improved by appropriately extending the distance from the ACPH to the cylinder. Based on the principle of maximizing the elastic range resistance of precast reinforced concrete beams, the formulas for calculating the optimal locations of ACPHs were established. [ABSTRACT FROM AUTHOR]

Damage of shear connectors in steel-concrete composite (SCC) beams affects the composite action and appears as abnormalities in the shear slip between the composite components. The shear slip at the composite interface causes nonlinearity in the global composite beam response which is an issue beyond the inherent complexity of the composite system. This paper presents a novel approach for damage detection of SCCs by variational mode decomposition (VMD) of shear slip data. Numerical and experimental studies were conducted on steel-concrete composite beams to generate noise-contaminated shear slip data from undamaged and damaged states of the structure. The VMD algorithm is employed to decompose shear slip signals into intrinsic mode functions (IMFs) and then, the center frequency of each mode is captured. The higher center frequency realized in the second mode is taken as a damage sensitive feature. Because IMFs curves are extracted from the signal splines interpolated between the average of the peaks and troughs, the change of energy in the center frequencies of the undamaged and damaged states can be defined as a damage index. Welch power spectral densities of the IMFs are calculated to further investigate changes in the center frequencies of IMFs obtained using the VMD algorithm. The empirical mode decomposition (EMD) technique is also utilized to decompose shear slip signals into IMFs for comparison purposes. The results show that the EMD is not able to detect abnormalities in the shear slip signals affected by damage because of losing information through several mode decompositions and a phenomenon termed mode mixing. However, when the VMD was set to decompose the signal into two IMFs, it was found that it is more efficient in maintaining the frequency content of the shear slip signal. According to the results, the proposed method has been proved successful in detecting damage of composite beams and can be employed as a reliable and robust technique. [ABSTRACT FROM AUTHOR]

Application of fiber-reinforced polymer (FRP) composites in the strengthening of reinforced concrete (RC) structures has become an increasingly accepted engineering practice. In particular, the use of externally bonded FRP wraps as a confining material for concrete can enhance both the compressive strength and the ultimate strain of concrete, making it suitable for strengthening and/or seismic retrofit of existing RC columns. This paper focuses on a recently developed analysis-oriented iterative FRP-and-steel confinement model for concrete and proposes a new optimization procedure to obtain an analytical expression for the corresponding monotonic envelope, reduce the associated computational cost, and increase the corresponding numerical robustness. Several analytical functions were evaluated in terms of their capability to fit the iteratively-generated stress-strain monotonic envelope for confined concrete. The newly proposed analytical formulation of the confined concrete stress-strain model was compared with the original iterative formulation in terms of computational cost for two examples of nonlinear seismic response analyses for: (1) an experimentally-tested concrete-filled FRP tube bridge column of a two-column bridge pier; and (2) a five-span bridge structure with FRP-retrofitted RC piers. It is found that the use of the newly proposed optimization-based analytical monotonic envelope can reduce by more than 30% the computational time associated with the original iteration-based monotonic envelope with negligible changes in the structural response prediction at both global and local levels. [ABSTRACT FROM AUTHOR]

In determining wind loads when designing buildings—especially high-rise buildings—wind speed is a critical factor. With increased progression of city high-rise construction, accurate prediction has become ever more important. Many factors, such as local climates, roughness of surrounding conditions, and terrain, may affect wind speed. But among all factors considered, terrain has a very large influence. Difficulties in reflecting the influence of terrain on wind speed include (1) collecting topographic data information; (2) quantitatively evaluating terrain features; and (3) expressing specific area relationships with surrounding observation stations. This paper poses means to solve these limitations by (1) using satellite imagery to gather topographic information; (2) evaluating terrain quantitatively with convolutional neural network (CNN)–based encoders; and (3) employing a graph neural network (GNN) to estimate the wind speed relationship of an arbitrary place to that of observation stations. Herein, a machine learning model utilizing the aforementioned means was proposed. To support this model, an experiment was conducted using observed wind speed data in Korea. Throughout the experiment, previous studies were used to compare results with ratification of the posed model. Given the submitted findings, further research and investigation to establish correlation with other experimental case results are proposed. [ABSTRACT FROM AUTHOR]

Low-rise wood buildings occupy over 95% of all residential structures in the US. However, low-rise buildings usually perform poorly during extreme wind events, such as hurricanes and tornadoes. To ensure the resilience of low-rise buildings to various loads, codes, specifications, and design manuals are usually adopted. However, wind loading in these design codes is typically represented by simplified wind pressure coefficients. Both the directional and envelope methods provided in the current standard consider explicitly the wind directions normal and parallel to the ridge of buildings, with the other directions enveloped for generalization purposes. In comparison, the database-assisted design (DAD) method, which has received increased attention from researchers, is characterized by the direct use of pressure time series from a large number of pressure taps measured in wind tunnel tests for various wind directions. Based on the several previous versions of the current standard, many researchers compared the wind pressures and peak responses from the DAD method and the directional and envelope methods in the current standard. Both methods were found to provide underestimated results. Currently, in addition to the absence of comparisons for the current standard, comparisons of the DAD method with the time-history analysis using the directional and envelope methods for a full-size building considering the material nonlinearity have not been performed. Moreover, the effects of wind speed and wind direction on the wind pressures and peak responses of structures have been ignored. In this paper, the results from both directional and envelope methods with time history analysis for low-rise residential buildings are assessed and compared with those from the DAD method. Synthetic hurricane tracks were incorporated based on the real wind speeds and directions in the community. Transient analysis with the time histories of wind pressures were applied to a realistic full-scale building model under different wind speeds and wind directions. The results suggest that the directional and envelope methods lead to an underestimated displacement, especially at high wind speeds. With wind directions parallel and normal to the ridge of buildings explicitly considered in the current standard, critical wind directions other than the two directions could not be detected, which could underestimate wind-induced responses. [ABSTRACT FROM AUTHOR]

Poor earthquake response in suspended ceilings can cause wide-scale injuries and financial losses, which underscores the need to understand such systems better. This paper presents a study on a plasterboard suspended ceiling system (PSCS) installed in a 3.00-m tall steel building. The PSCS is an assembly of a plasterboard with plan dimensions of 2.69 m×2.27 m attached to a horizontal metal frame suspended from the roof. The building was subjected to Taft motion in the principal horizontal directions. The peak input accelerations ranged between 0.05g and 0.25g (0.05g and 0.70g) in the short–edge (long-edge) direction; the natural period of the PSCS increased from 0.91 to 0.99 s (0.32 to 0.99 s) during the tests. The peak plasterboard acceleration ranged between 1.1 and 2.4 times the peak roof acceleration (except during impact). Damage was observed primarily in the suspender struts near its lower end, attributable to the "rigid" connection between strut and horizontal metal frame. Response of the PSCS in the "softer" direction was greater and more sensitive to the response of the superstructure compared to the orthogonal direction. Static tests on the joint between the suspender and the roof of the building provided information for the development of the numerical model. Separate models were developed for the two principal horizontal directions due to different degradation characteristics. An ambient damping of 2% in the numerical model (experimental value was 8%) led to a much better simulation in the "softer" direction, indicating that damping during "large-amplitude motions" can be considerably less than that during "low-amplitude motions." [ABSTRACT FROM AUTHOR]

The capability of the wave method for structural health monitoring, based on fitting a layered Timoshenko beam by waveform inversion of impulse responses, to localize damage is investigated using shake table experiment data. The specimen is a full-scale slice of a seven-story reinforced concrete (RC) shear wall building, which was tested on the University of California San Diego–Network for Earthquake Engineering Simulation (UCSD-NEES) outdoor shake table under consecutive exposure to four earthquake motions with increasing intensity, which progressively damaged the structure. The damage is localized by partitioning the beam into horizontal layers, comprising a single floor in the parts with the most severe damage and a group of floors in the lightly damaged parts, and detecting changes in the wave velocities in each layer with respect to a reference state. Small amplitude, ambient vibration response data were used as input for the inversion. The paper describes a number of improvements in the methodology, which were necessary to improve the quality of the inversion, the success of the method to detect the existence and the intensity of the damage in different parts of the structure, and how it fared in comparison to other methods applied to the same test structure. Also, recommendations are proposed for future improvements of the method. [ABSTRACT FROM AUTHOR]

Rebar cages are commonly used in reinforced concrete constructions. These cages consist of longitudinal and transverse reinforcing bars usually connected by tie wires. Numerous incidents of rebar cage failure and collapse have been reported at construction sites, often leading to injuries, fatalities, construction schedule delays, and added costs. Using mechanical connectors such as U-bolts instead of tie wires can improve stability and strength of rebar cages. This paper aims to investigate the mechanical behavior of U-bolt connections through experimental tests and to explore the potential application to rebar cages through analytical models. Experiments were conducted on U-bolt connectors to determine the force-deformation response behavior in different degrees of freedom and for different rebar conditions. Then, the data obtained from a previously completed experimental study on a full-scale tie-wired rebar cage were used to develop and calibrate a nonlinear finite-element model of the test specimen. The force-deformation response of U-bolt connections was then included in the model, replacing the tie wires, to investigate the effect of mechanical connectors on the lateral stiffness and strength of the rebar cage. The results showed that application of mechanical connectors for cross-bar connections in the rebar cages can increase the lateral strength of rebar cages, rendering U-bolt connectors as a potential solution to improve stability and safety of rebar cages. [ABSTRACT FROM AUTHOR]

This paper presents an in-situ study of imaging cracks in the Berwick Bay Bridge nondestructively by the application of an inverse algorithm to ultrasonic coda wave measurements. Using only five sensors to collect coda signals, we have monitored a 100×70×33 cm3 volume of the bridge subjected to a sequence of static load tests, without prior knowledge of cracks. Whereas spatiotemporal waveform decorrelations can indicate global damage conditions, our inversion algorithm produced a three-dimensional map of change density that revealed the location and lengths of multiple 0.1-mm-scale cracks in reinforced concrete. [ABSTRACT FROM AUTHOR]

This paper presents a case study of a realistic application and evaluation of a promising structural health monitoring approach that exploits some topological features of building-like structures to develop a reduced-order, reduced-complexity, not-necessarily-linear, substructure model. The approach not only reliably detects the occurrence of anomalous features that can reflect incipient damage and deterioration but also provides the locations of the structure's regions where a single or multiple changes have been detected. The target structure used in this study is a 52-story building in Los Angeles that is instrumented with a relatively dense sensor array and is being continuously monitored through the efforts of the community seismic network (CSN). Two qualitatively different system identification approaches (global and substructuring) are applied to the large data set of ambient acceleration measurements produced by a strong wind event ("Santa Ana winds") to identify the dominant modal characteristics of the building. The results are shown to match the corresponding results from a high-resolution computational model of the building based on a widely used structural analysis software package (ETABS) developed by Computers and Structures, Inc. The main contribution of this study is to demonstrate the practical feasibility of the proposed substructuring approach with a high-order system using both wind and low-amplitude ambient vibration measurements. The approach also assesses the accuracy and reliability of the estimates of the dominant modal features of the structure to subsequently provide a probabilistic measure of confidence in the extent and location of changes if an anomaly is detected. Due to the minimal computational resources needed to implement the proposed substructuring approach, it is efficient for near-real-time applications where important structures need to be continuously monitored for sustainability as well as resiliency requirements. The method is applicable to linear, nonlinear nonhysteretic, and hysteretic systems, with no restriction on the source of the signal for identification purposes. [ABSTRACT FROM AUTHOR]

The existing machine learning (ML) models for vibration-based damage assessments often use highly compressed features or are restricted to preprocessed signals with fixed durations and sampling rates. Additionally, the learning capacities of ML models and computational resources are limited, which restricts using raw signals as direct input. This paper studied Mel filter banks (MFBs) for seismic signal processing, inspired by speech recognition technology. It is argued that the same filter designs in audio engineering may not be appropriate for seismic records, and therefore, a customized filter bank formulation was developed. Hybrid deep learning models for rapid assessments (HyDRA) were introduced as multibranch neural network architectures that enable end-to-end training for different types of processed vibration data structures. Moreover, the performance-based earthquake engineering (PBEE) equation was adjusted to integrate ML model uncertainties for probabilistic assessments. The proposed concepts were validated in a case study based on a data set of 32,400 nonlinear time-history analyses of a highway bridge in California. Insights and guidelines are provided for optimum filter design based on 5,184 experiments. Several HyDRA architectures were compared with benchmark models. The optimized MFB feature type outperformed features obtained from continuous wavelet transform and a stacked vector of conventional earthquake engineering indexes. A Bayesian variant of HyDRA was investigated to showcase its integration in the modified PBEE equation. Adopting custom filter banks with the HyDRA architecture enables effective feature extraction from raw vibration records by diversifying feature space and preserving information in the time and frequency domains. [ABSTRACT FROM AUTHOR]

This paper presents experimental testing on glulam beam–column moment-resisting connections using glued-in rods (GiRod) and compares the results with model predictions. Three connection geometries and varying numbers of rods and member size were tested and compared. This experiment will be helpful in grounding research by bringing in new experimental results and proposing an innovative experimentation method. Experimental results showed the high efficiency of glued-in rod connections to transfer loads and bending moment between spruce pine glulam timber members. The observed limit states of the connections were failed steel rods in ductile tensile yielding or wood splitting around the anchorage installed perpendicularly to the grain in the column. It was found that the tested connections behaved as a semirigid moment-resisting connection and exhibited a ductile failure mode when wood splitting was avoided by design. Comparison of experimental results with model predictions showed good agreement, with a deviation under 15% for the moment capacity of the connection. [ABSTRACT FROM AUTHOR]

This paper presents the experimental results from nine full-scale concrete-filled double-skin tubular (CFDST) beam-columns. The test specimens exploited two fabrication strategies, featuring either hollow steel inner skins with corrugated geometry or ultrahigh-strength steel corner tubes to enhance the seismic performance of noncompact CFDST beam-columns for potential use in low-to-moderate seismicity regions. The effects of loading sequence, axial load ratio, and cross-sectional geometry were investigated. The experimental results suggested that the current AISC specification may be used to predict the axial strength of composite members with a relatively good accuracy. In the postbuckling range, conventional CFDST beam-columns and those with corrugated inner skins are prone to fracture at the corner welds of the built-up cross section. However, the latter exhibited up to two times larger drift capacities than conventional CFDST counterparts prior to losing axial load carrying capacity. Noncompact beam-columns retrofitted with ultrahigh-strength steel corner tubes exhibited a 4% lateral drift demand without experiencing more than 25% flexural strength loss. The presence of ultrahigh-strength steel increases the plastic hinge length of CFDST beam-columns by up to four times relative to CFDST beam-columns with corrugated inner skin, regardless of the employed loading history. [ABSTRACT FROM AUTHOR]

Endplate moment connections with shape memory alloy (SMA) bolts provide self-centering for the seismic resilience of structures. Predicting the self-centering response of these new beam–column connections, which have not been codified yet, requires conducting experimental tests or detailed continuum finite-element simulations. Computationally efficient predictive tools are needed to facilitate the analysis, design, and assessment of self-centering connections and moment frames. In this paper, artificial neural networks (ANNs) are used to develop a MATLAB tool for predicting the moment-rotation backbone and self-centering response of extended endplate connections with SMA bolts. As the input for the neural networks, the predictive model development employs a design database of response parameters from 72 finite-element (FE) models and experimental tests of seven beam–column connection specimens. Neural networks are trained for seven response parameters, and the trained networks are used to develop a graphical user interface (GUI). The coefficient of determination for the trained ANNs is in the range of 0.92 to 0.99, indicating acceptable prediction accuracy. Furthermore, optimization studies using a multiobjective genetic algorithm are performed, seeking the minimization of material use (steel and SMA) and improved connection-response characteristics (i.e., stiffness, strength, and ductility). A phenomenological model of SMA connections is also developed in OpenSees. The use of the ANN-based predictive tool for accurate and efficient modeling of SMA-based connections and self-centering moment-resisting frames is illustrated. The computation time for predicting the moment-rotation response of a typical SMA connection is significantly reduced from seven hours in ANSYS to only three minutes in OpenSees while providing the same level of response prediction accuracy. Furthermore, the optimization results are confirmed by performing nonlinear pushover and response history analyses. [ABSTRACT FROM AUTHOR]

Peridynamics (PD) has been increasingly used to study the damage behaviors of reinforced concrete (RC) structures due to its strong capacity in analyzing discontinuous problems. In this paper, bond-based peridynamics (BPD) is enhanced for refined analysis of bond-slip behaviors between concrete and ribbed steel rebar in the pullout test. The enhancement of BPD includes the following: (1) an axial-shear interaction (ASI) model for refined simulation of bond-slip behaviors between steel ribbed rebar and concrete; (2) a nonlinear uniaxial concrete model to avoid excessive compression of concrete bonds; (3) a novel gradually weakening fictitious element (GWFE) approach to improve the stability and convergence of the Newton algorithm in solving the PD equations, e.g., in case of negative concrete stiffness; (4) a horizon updating approach for rebuilding bond interactions when large displacements occur in the bond-slip process; and (5) a parallel computing approach to improve the computational efficiency of refined analysis. The enhanced BPD method is implemented in an open-source finite-element software, OpenSees, and verified by a rebar pullout test. The type of steel rebar rib, strength of concrete, cross-area of steel, and cyclic loading condition are investigated in detail regarding their effects on the stress redistribution and mesoscale crack propagation of the RC members. The results demonstrate that the enhanced BPD modeling method presented herein is capable of fine simulation of bond-slip behaviors in the pullout test, e.g., the strength deterioration, stiffness degradation, and cyclic response. [ABSTRACT FROM AUTHOR]

The paper studies the flexural responses of one-way reinforced concrete structural elements subjected to cased explosive charges to explore the suitability of using high-strength materials for such scenarios. The detonation of cased explosive charges leads to the generation of fragments due to the rupturing of the casing housing the high explosive charge. Consequently, structures subjected to the detonations of cased explosive charges are acted upon by both the blast wave (due to the detonation of the high explosive charge) and the fragments. This study was motivated by the fact that although similar studies have been conducted to explore the suitability of using high-strength materials for scenarios involving bare (uncased) explosive charges, such studies are still uncommon when it comes to cased explosive charges. The methodology adopted herein consisted of developing a semianalytical approach that was validated against (1) the results of experimental static tests available in the literature, (2) the results of experimental blast trials conducted with bare (uncased) explosive charges that are available in the literature, and (3) the results of finite-element simulations, conducted by the authors due to the nonavailability of a relevant experimental data set in the public domain pertaining to cased explosive charges (to the best of the authors' knowledge). Following the validations, the adopted semianalytical approach was further used for conducting detailed parametric investigations. It was observed that compared with the lightly cased explosive charge (casing to charge mass ratio=0.5), the peak structural displacements for the heavily cased explosive charge (casing to charge mass ratio=1.5) showed an increase of 50% (for high-strength materials) to 64% (for normal-strength materials). Moreover, compared with normal-strength materials, the application of high-strength materials was also noted to reduce the peak structural displacements by 9% to 23%, which indicated the increased measure of safety provided by the high-strength materials. In addition to this, compared with normal-strength concrete, the employment of high-strength concrete grades was also effective in limiting the fragment inflicted damage by 25% to 36%. Additionally, increasing the reinforcement ratio to 0.65% from 0.16% effectively reduced the peak structural displacements by 57% to 63%. [ABSTRACT FROM AUTHOR]

This paper presents the evaluation of two methods for manually estimating the elastic lateral-torsional buckling (LTB) resistance of general doubly and singly symmetric I-section members having a linear variation in the web depth. The study focuses on unbraced lengths having idealized torsionally simply supported (fork) end conditions. The first method uses cross-sectional properties at the midspan of the unbraced segment along with a moment gradient modifier equation, written in terms of the flange stresses, to develop its strength approximation. This approach is employed in the first edition of the AISC-MBMA Design Guide 25 (DG 25). The second method is an extension of an approach that has been shown to be accurate and efficient for prismatic doubly and singly symmetric I-section members and is recommended in the second edition of DG 25. This approach uses cross-sectional properties at a critical section within the unbraced length, defined as the cross section where the ratio of the moment demand to the base LTB resistance in uniform bending is maximum, along with a moment gradient modifier equation written in terms of the above maximum ratio and the corresponding ratios at the quarter points of the unbraced length. Furthermore, Method 2 employs an additional calibration factor that accounts for an apparent destabilizing effect of the inclination of the shear center with respect to the axis of torsional restraint. The predictions from these methods are evaluated by an extensive parametric study encompassing the full design space for I-section members with linearly-varying web depth, as defined by DG 25. The second method is shown to provide improved accuracy, avoiding undesirable nonconservative errors in certain situations. The calibration factor developed as part of the second method is shown to eliminate undesirable errors in the first method as well, providing streamlined and accurate buckling estimates for linearly tapered member unbraced lengths. [ABSTRACT FROM AUTHOR]

The choice of spectral targets for ground motion selection has a strong impact on structural demands resulting from nonlinear time history analysis. In particular, the conditional mean spectrum (CMS) has been recognized as an appealing alternative to the uniform hazard spectrum (UHS) as a spectral target due to the former's more realistic shape and reduced conservatism. Using a tall building case study in a high-seismicity region, this paper evaluates the building demands generated by UHS- and CMS-based selection procedures. Theoretically rigorous implementation of CMS-based selection using 17 different conditioning periods is shown to reduce maximum considered earthquake (MCE)–level demands on the case study building by 9%–35% relative to UHS-based selection. Furthermore, the simplified CMS-based procedure in the building code with apt choice of only two conditioning periods is found to satisfactorily capture the demands generated by the theoretically rigorous approach. Findings also highlight the degree of sensitivity of CMS-based results to the choice of conditioning periods and to enforcement of lower bounds on spectral targets, such as 75% of the UHS. The presented analysis procedure can be replicated in future studies for explicit evaluation of simplified CMS ground motion selection in other structural systems or analysis cases. Since its introduction to the building code, the alternative, conditional mean spectrum-based method for ground motion selection has gained traction among practitioners due to its reduced conservatism relative to traditional selection methods. To simplify the implementation of conditional mean spectra in practice, the building code alternative method requires a minimum of only two target spectra be used, so long as their envelope satisfies a lower bound within a specified period range. However, there are few quantitative studies of the impacts of these simplifications on the resulting building demands. In this study, we demonstrate how building demands vary when a tall building in a high-seismicity region is analyzed using either a traditional or a conditional mean spectrum-based selection approach. We find that using two reasonable target spectra in accordance with the alternative method produces acceptable building demands as compared to the demands obtained from performing exhaustive nonlinear analysis with a large number of target spectra. Furthermore, we illustrate how different choices of conditional mean spectrum targets maximize different types of building demands (e.g., interstory drift, base shear, floor acceleration) and how some types of demands are more sensitive to this choice than others. This work provides a procedure for evaluating conditional mean spectrum-based ground motion selection that can be replicated in the future for other buildings or structural systems. [ABSTRACT FROM AUTHOR]

This paper uses nonlinear analysis to determine the impact of corrosion-induced damage on the load-carrying capacity of prestressed concrete bridge girders. The analyses rely on two types of models, namely, beam models and nonlinear truss models. The latter are deemed necessary to obtain reliable estimates of the shear capacity, as beam models are not well-tailored for capturing shear failures. A procedure to account for the reduction in area and deformability of corroded strands, based on visually observed corrosion damage, is proposed and implemented. The models are calibrated and validated with the results of experimental tests on prestressed girders, which exhibited varying levels of corrosion-induced damage. Further analyses allow the comparison of the capacity of corrosion-damaged girders to that of their undamaged counterparts. The accuracy of a simplified procedure, using equations in the AASHTO code to determine the flexural and shear capacity of the damaged girders, is also determined. [ABSTRACT FROM AUTHOR]

It is known that the performance of traditional passive tuned mass dampers (TMDs) is highly sensitive to vibration frequency. The fundamental frequency of existing tall buildings may shift to lower value due to damage or other reasons. In this regard, this paper deals with the resultant detuning problems of a traditional passive TMD for vibration control by retrofitting it with a passive adaptive negative stiffness device (NSD). The applied NSD not only provides negative stiffness for adjusting the TMD's de-tuned stiffness at its working stage, but also offers a fail-safe limiting stop for the TMD at large deformation/stroke. In this study, compared to the original TMD, a novel TMD-NSD assembly is proposed that is shown to be more effective for serviced structures. For example, the original TMD can only provide about 2.83% additional damping ratio to frequency-changed structures, while the newly proposed TMD-NSD further improves the damping ratio to 5.34%. Moreover, in the study it is found that the TMD-NSD also outperforms the TMD in resisting dynamic lateral loading such as along winds, cross winds, and earthquakes. [ABSTRACT FROM AUTHOR]

Structural health monitoring (SHM) based on global navigation satellite systems (GNSS) is an interesting solution to provide absolute positions at different locations of a structure in a global reference frame. In particular, low-cost GNSS stations for large-scale bridge monitoring have gained increasing attention these last years because recent experiments showed the ability to achieve a subcentimeter accuracy for continuous monitoring with adequate combinations of antennas and receivers. Technical solutions now allow displacement monitoring of long bridges with a cost-effective deployment of GNSS sensing networks. In particular, the redundancy of observations within the GNSS network with various levels of correlations between the GNSS time series makes such monitoring solution a good candidate for anomaly detection based on machine learning models, using several predictive models for each sensor (based on environmental conditions, or other sensors as input data). This strategy is investigated in this paper based on GNSS time series, and an anomaly indicator is proposed to detect and locate anomalous structural behavior. The proposed concepts are applied to a cable-stayed bridge for illustration, and the comparison between multiple tools highlights recurrent neural networks (RNN) as an effective regression tool. Coupling this tool with the proposed anomaly detection strategy enables one to identify and localize both real and simulated anomalies in the considered data set. [ABSTRACT FROM AUTHOR]

Pinching characterizes the hysteretic response of several structural systems. It is associated with a reduced dissipated hysteretic energy under cyclic loading and can significantly affect seismic performance, especially under repeated earthquakes. Although several scholars proposed advanced joint arrangements with reduced pinching, ordinary timber structures present pronounced pinching effects due to the local damage to the timber joints. This paper quantifies the impact of variable pinching on the seismic performance of a timber structural archetype. The authors modeled the hysteretic response of a light-timber framed assembly using an empirical hysteresis model and assessed the sensitivity of the displacement demand of the chosen archetype to pinching, number of earthquake repetitions, and spectral acceleration. The choice of an elementary structural archetype, rather than a more complex system, allows isolating the effects of pinching, which could otherwise be disguised by other phenomena, like force redistribution between structural assemblies due to plasticization. [ABSTRACT FROM AUTHOR]

From the post-war period to present day, economic development and urbanization have led to various demands for infrastructure, including bridges and viaducts. However, especially in recent years, there have been reports of sudden and unexpected collapses of bridges and viaducts, associated with large economic losses and, unfortunately, loss of human lives. The study of the causes that have led to these disasters is of strategic importance because it allows for the deepening of the specific technical knowledge. For this reason, this paper presents the study of the causes that led to the collapse of one of the spans of the "La Reale" viaduct in the Piedmont region in Italy. The main reason for the collapse was to be found in the incorrect injection of cables, which led to the absence of grout inside the sheaths for a length equal to one third of the deck. In this region, cables were subjected to a highly aggressive environment with severe corrosion. This resulted in fragile failure of the deck, with no signs that could suggest such important structural problems during normal inspection operations. The only evidence was some white efflorescence. However, in light of the knowledge prior to the present study, this evidence could not be easily connected to the type of phenomenon in progress that led to the collapse. Based on the experimental tests carried out on the collapsed portion, this study highlights new symptoms not associated with any structural pathology previously studied. The main concern relative to the structural safety assessment in cases such as the one presented in this study is related to the lack of evidence on the current state of cable degradation. Therefore, objective data for numerical evaluations is coming from bridge load tests. In this regard, the evaluation of a partial safety coefficient of variable traffic loads according to two different approaches based on bridge load tests and safety factors suggested by structural codes is presented. [ABSTRACT FROM AUTHOR]

Stiffness modifiers are used in linear structural analysis programs to recognize the low-strain amplitude nonlinear material stress–strain response and support the design of reinforced concrete structures. For example, stiffness modifiers are used to account for the reduction in stiffness that results mainly from crack development and propagation, bar bond slip between cracks, and bar bond slip of the longitudinal reinforcement developed beyond the column ends. This paper presents a primarily mechanistic model to compute the stiffness modifiers for reinforced concrete rectangular columns to support the seismic design of reinforced concrete structures. The model accounts for five modes of deformation found in columns and is calibrated against a database of test results reported in the literature on 38 large-section columns that exhibited ductile response. The paper also describes a simplified equation for use in seismic design. The simplified equation was calibrated through an extensive parametric analysis of the model. The mean, median and coefficient of variation of the ratios of the stiffness modifiers computed from the recorded response of test columns and the model output were 1.02, 1.00, and 0.18, respectively, and those calculated by the simplified equation for the same ratios were 0.95, 0.98, and 0.18, respectively. [ABSTRACT FROM AUTHOR]

Structural assessment and seismic vulnerability of ancient masonry buildings is a difficult task even when employing advanced specialized technical skills, which requires a complex study. This paper aims to assess the structural and seismic safety of the Esfahan Shah Mosque in Iran by numerically investigating the nonlinear behavior of the mosque for different scenarios and identifying if there is a correlation between crack patterns resulting from numerical analysis, inspection, and historical evidence. First, the numerical model of the mosque is developed and updated using the experimental parameters obtained from a nondestructive test (NDT) campaign that included ambient vibration and sonic testing. Second, the finite element calibrated model is used to evaluate the structural behavior of the mosque under vertical loading, including the influence of the soil and a sensitivity analysis varying the masonry material properties. Besides, the paper discusses the structural behavior of radial stiffening walls that connect the inner and outer domes of the mosque. Finally, pushover analysis was performed to assess the seismic safety of the building and the efficiency of the structural strengthening implemented in the early 20th century. The different technical observations and analyses lead to a better understanding of the double dome and the eyvan (a rectangular space, usually vaulted, walled on three sides, with one end entirely open) as the most vulnerable parts of the structure, which validates the structural strengthening of the 1930s. Yet, improving the connection between the stiffening walls and the two domes could effectively increase the global structural performance of the building. [ABSTRACT FROM AUTHOR]

Structural health monitoring provides a measurement-informed quantitative and systematic framework to better assess the state of fatigue in aging infrastructure. In this paper, a general methodology for probabilistic modeling of fatigue damage accumulation is presented from a structural health monitoring perspective, which allows for estimating the remaining fatigue life from strain measurements. The method presented uses a damage-sensitive feature derived from the Palmgren–Miner rule—a commonly used measure in fatigue analysis and design—as a surrogate for degradation and probabilistically models the process of degradation. A Bayesian approach is employed to estimate the parameters of this degradation model, and the remaining fatigue life is predicted using Markov chain Monte Carlo (MCMC) simulations. In the simplified case of constant stress amplitude, an analytical solution for the fatigue life has been derived. Moreover, techniques are presented to account for various challenges such as the lack of structural health monitoring data (SHM) for the initial unmonitored period and the absence of the continuous monitoring program. The main contribution of the paper is to develop a probabilistic degradation modeling framework using a damage-sensitive feature derived from the Miner rule for the prediction of the remaining fatigue life of critical bridge components. A numerical case study is presented to demonstrate the proposed methodology, and the major challenges of its implementation in the field are demonstrated through illustrations. [ABSTRACT FROM AUTHOR]

This paper presents an iterative sandwich beam theory (ISBT) and a simplified version suitable for the design termed simplified sandwich beam theory (SSBT) used to predict the elastic mechanics of partially composite insulated concrete sandwich wall panels (SWPs) under flexural, axial, and thermal loads. These solution methods expand upon closed-form solutions to create a more general analysis technique. Design and analysis of SWPs are handled largely outside of codified documents and are almost exclusively designed such that they will remain within the elastic range. The presented ISBT and SSBT methods have been used in the United States precast industry since 2017 and are implemented in widely available software, LECWall, as of 2020, for predicting elastic deflections and stresses. In this paper, the ISBT and SSBT solution methods are validated with experimental data from the literature and using finite-element analysis. For the ISBT cracking moment and deflection, the measured-to-predicted ratio were 0.99 and 1.0 with coefficients of variation (COVs) of 0.10 and 0.11, respectively. For the SSBT cracking moment and deflection, the measured-to-predicted ratio was 0.99 and 0.99 with COVs of 0.21 and 0.19, respectively. For thermal loading, the ISBT and SSBT deflection m easured-to-predicted ratios were 0.95 and 0.90, respectively. The model was then used to investigate the behavior of sandwich wall panels under varying load combinations and with various section and material properties to demonstrate the robustness of the presented methods. [ABSTRACT FROM AUTHOR]

This paper, which is the second of two companion papers, presents the results of a large-scale testing program on a novel bridge column design, termed polyurethane (PU)-enhanced rocking column with energy dissipation (ED) links. The experimental program included cyclic testing of large-scale (approximately 1∶2.5) cantilever bridge columns, including (1) a rocking-only precast concrete column, which served as the reference column, (2) a PU-enhanced rocking column with a solid PU segment, and (3) a PU-enhanced rocking column with an axisymmetrically bilayered segment with an exterior PU layer to withstand seismic loads, an internal reinforced concrete core to sustain long-term gravity loads, and external ED links to provide energy dissipation and flexural stiffness and strength. The specimens were subjected to displacement-controlled lateral cyclic loading of increasing amplitude (exceeding a 10% drift ratio) at several drift ratio rates (up to 1 s−1). The tested PU column with ED links was further repaired via ED link release and retightening—the yielding of the ED links was small and did not justify replacement—to demonstrate its rapid reparability characteristics. The repaired column was subsequently retested to demonstrate that the original column properties had been practically recovered. This second companion paper experimentally quantifies the performance of all designs in terms of strength, ductility capacity, self-centering and energy dissipation capabilities, posttensioning losses, and ED link fracture capacity. It also quantifies the capability of ED link release and retightening (and, by extension, ED link replacement) in eliminating residual deformations and recovering the mechanical properties of the original/undamaged system. Compared to conventional RC rocking-only columns, the proposed PU-enhanced column design with ED links demonstrated higher energy dissipation and self-centering capabilities, while release and retightening of the ED links eliminated the residual deformations and resulted in the recovery of the mechanical properties of the original/undamaged column. While ED link release and retightening (i.e., ED link reuse) is adopted in this study, because the yielding of the ED links was small, as verified herein by the practically identical response of the original and repaired column, it can be deduced that ED link replacement (i.e., use of new/pristine ED links) would also restore the original column properties and eliminate residual deformations. [ABSTRACT FROM AUTHOR]

This paper, which is the first of two companion papers, investigates the performance of a novel bridge column design, termed polyurethane (PU)-enhanced rocking column with energy dissipation (ED) links, through a large-scale testing program. The proposed column design offers explicit damage control via damage-resistant end segments made of PU, ED and flexural strength/stiffness through ED links, and self-centering through internal unbonded post-tensioning. The PU segments have high deformability, allowing large lateral column deformations with negligible damage. The ED links are in the form of buckling-restrained bars made of high-performance steel and offer hysteretic damping and flexural stiffness and strength to reduce the seismically induced displacement demands. The experimental program included cyclic testing, at various loading rates, of large-scale (approximately 1:2.5) PU-enhanced cantilever rocking columns with two designs for the PU segment: (1) solid PU segment, and (2) axisymmetrically bilayered segment with an exterior PU layer to withstand seismic loads and an internal reinforced concrete core to sustain long-term axial service loads and provide resistance against creep. The specimens are subjected to displacement-controlled lateral cyclic loading of increasing amplitude (exceeding a 10% drift ratio) at several drift ratio rates (up to 1/s). A tested column is repaired via ED link release and retightening to demonstrate their rapid reparability characteristics and are retested to demonstrate the recovery of the original column properties. While ED link release and retightening (i.e., ED link reuse) is adopted in this study, because the yielding of the ED links was small as verified in the second companion paper by the practically identical response of the original and retrofitted column, it can be deduced that ED link replacement (i.e., use of new/pristine ED links) would also restore the original column properties. A rocking-only precast concrete column is also tested under the same loading protocols to serve as reference for comparisons. This first companion paper outlines the experimental program, quantifies the observed damage of the proposed column design for a range of seismic hazard intensities and compares it with that of the rocking-only column, and validates the capability of ED link release and retightening (and, by extension, ED link replacement) as a repair method that recovers the damage resistance/avoidance properties of the original system. Compared to conventional RC rocking columns, the proposed column design demonstrated significantly higher resistance against damage in terms of concrete spalling and crushing. [ABSTRACT FROM AUTHOR]

Complementing a companion paper that summarizes the building global response and physical damage of a midrise cold-formed steel (CFS) framed building during an earthquake and postearthquake fire test program, this paper focuses on understanding the seismic behavior of the shear walls utilized in the building system during this test program. In contrast to shear walls tested in an isolated configuration, the shear walls within the full-scale test building were constructed and tested under real-world kinematic constraints and dynamic loading environments. The shear walls located at various planar and vertical locations of the test building were instrumented with a dense array of analog sensors to monitor the shear wall local responses. In this study, the shear wall local responses are correlated with the global responses of the building to advance understanding regarding the behavioral characteristics of individual shear walls and in particular the interactions of the shear walls as part of the lateral-load-resisting system. Important seismic design parameters are inferred from the measured building response using a parameter optimization strategy. Their implications associated with the seismic design of CFS wall-framed structural systems are discussed in relation to code provisions and design guidelines. [ABSTRACT FROM AUTHOR]

To advance understanding of the multihazard performance of midrise cold-formed steel (CFS) construction, a unique multidisciplinary experimental program was conducted on the Large High-Performance Outdoor Shake Table (LHPOST) at the University of California, San Diego (UCSD). The centerpiece of this project involved earthquake and live fire testing of a full-scale 6-story CFS wall braced building. Initially, the building was subjected to seven earthquake tests of increasing motion intensity, sequentially targeting service, design, and maximum credible earthquake (MCE) demands. Subsequently, live fire tests were conducted on the earthquake-damaged building at two select floors. Finally, for the first time, the test building was subjected to two postfire earthquake tests, including a low-amplitude aftershock and an extreme near-fault target MCE-scaled motion. In addition, low-amplitude white noise and ambient vibration data were collected during construction and seismic testing phases to support identification of the dynamic state of the building system. This paper offers an overview of this unique multihazard test program and presents the system-level structural responses and physical damage features of the test building throughout the earthquake-fire-earthquake test phases, whereas the component-level seismic behavior of the shear walls and seismic design implications of CFS-framed building systems are discussed in a companion paper. [ABSTRACT FROM AUTHOR]

This paper focuses on the simulation of irregular stone masonry by the lattice discrete particle model (LDPM), which simulates the fracture and failure behavior of quasi-brittle heterogeneous materials by modeling the interaction among coarse material heterogeneities. LDPM is formulated at the length scale of the masonry stones whose interaction is described through constitutive equations featuring softening in tension and strain hardening in compression. The numerical results relevant to diagonal compression tests show that the intrinsic stochastic character of LDPM can quantify the variation of the mechanical properties of irregular masonry resulting from random stone size and stone-size distribution. Furthermore, the paper presents an analysis of the size effect on irregular stone masonry structures. This was obtained by simulating the shear behavior of geometrically similar samples of different sizes. The simulations demonstrate that increasing structural size leads to a significant reduction of both structural strength and structural ductility. The magnitude of the predicted size effect suggests that, contrary to typical experimental results on reduced size samples, real irregular masonry structures must be considered as perfectly brittle. [ABSTRACT FROM AUTHOR]

The number of studies on ultrahigh-performance concrete (UHPC) or ultrahigh-performance fiber-reinforced concrete (UHP-FRC) for more resilient and sustainable reinforced concrete (RC) structures has rapidly increased in recent years due to the superior mechanical and durability properties of UHPC. The application of UHPC as a replacement for conventional concrete materials in various RC elements necessitates a thorough understanding of the structural behavior of the reinforced UHPC (R/UHPC) components under various types of loadings. This paper presents a systematic review of the state-of-the-art developments in R/UHPC elements. It addresses various topics including beams, columns, beam–column joints, shear walls, bridges, structural retrofitting, and applications such as seismic and impact. Due to the ultrahigh tensile, compressive, and bond strengths, unique strain-hardening behavior, and ductility of UHPC, R/UHPC structures may exhibit substantially different behavior than conventional RC structures at both the component and system levels. This implies that particular attention must be paid when design and analysis approaches for conventional RC elements are applied to R/UHPC elements, and suggests that developing new design philosophies is warranted to take advantage of UHPC's unique mechanical properties. The present paper summarizes the developments in analysis and design approaches for R/UHPC elements under axial forces, shear forces, and bending moments, and highlights the advantages and limitations of these approaches. Important design considerations for effectively utilizing UHPC in structural elements are also suggested. In addition to normal-strength steel reinforcing bars, the potential for reinforcing UHPC with high-strength steel bars, fiber-reinforced polymer components, and structural steel shapes is discussed based on the results of pioneering studies. Finally, this paper identifies challenges and suggests future directions for research on UHPC in structural engineering. [ABSTRACT FROM AUTHOR]

Steel-concrete composite columns are strong and efficient structural members. However, their strength is not consistently recognized within design standards. In particular, current provisions regarding the strength of composite columns under combined axial compression and biaxial bending are overly simplistic and conservative. This paper presents a study of the biaxial behavior of square and rectangular, filled and encased composite columns and methods of evaluating their strength. Analyses of composite cross sections confirm the conservative nature of current design provisions and form the basis for modified strength equations that better capture the shape of the three-dimensional interaction surface. Analyses of composite columns confirm that the proposed design equations are suitable for use within the direct analysis method for evaluating members with length effects. The proposed design equations are further validated against published experimental results. This paper provides key insights on the behavior of composite columns subjected to axial compression and biaxial bending and offers an improved yet practical method of evaluating strength under these conditions that will enable more efficient designs. [ABSTRACT FROM AUTHOR]

Space trusses are extensively used to construct large free spans in roofs. In many countries, connections in such space trusses are made with tubes linked by typical space-truss connections. Typical nodes are made with the superposition of flattened tube ends significantly reducing the strength of such space trusses. This paper presents the use of natural sisal fiber and the reuse of recyclable tires to produce spacers to correct such typical nodes. The choice of those new materials reflects the growing interest in recycling, reducing, and reusing usable waste. There is increasing global environmental awareness of and social concern with the high rate of petroleum resource depletion as in tire manufacture. Moreover, the new environmental and sustainability regulations in engineering arouse interest in new and natural materials like sisal fibers. Therefore, in this paper, two new spacers are presented as an appropriate choice to reduce the eccentricity of typical connections in space trusses. The results of experimental and numerical tests show their efficiency in reducing the eccentricities of typical nodes, increasing the resistance capacity of space trusses with low cost materials. Finite-element (FE) results are compared with experimental results validating the advantages of using these new spacers in typical connections in space-truss nodes. [ABSTRACT FROM AUTHOR]