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• Propose a simplified model for CLT wall lateral behavior under varying boundaries. • Demonstrate proposed model's accuracy and limitations via experiments. • Illustrate how wall configurations and boundary conditions impact on CLT behavior. A new simplified mechanistic model was developed in this study to predict the rocking and sliding lateral response of a CLT panel wall under monotonic pushover with different boundary and gravity loading conditions based on an approximation of the principle of virtual work. Namely, for a given forced lateral displacement increment, the CLT wall will engage in a combination of rocking and sliding motion that will minimize the total work needed to go through that displacement increment. The proposed model was compared to the existing test results to illustrate its ability to capture the two types of wall behavior. Being a simplified mechanistic model, a number of material nonlinear characteristics such as the local crush of wood and the biaxial interaction of the connectors were not captured, resulting in a backbone characterization accuracy not as good as some existing well-calibrated models. However, the contribution of the study is to provide a mechanistic approach to address the switching between rocking and sliding behavior of CLT panelized walls under different boundary conditions. Using the model, a sensitivity analysis was conducted to investigate the effect of wall configurations and boundary conditions on the behavior of CLT shear walls. [ABSTRACT FROM AUTHOR]

Cross Laminated Timber (CLT) is a relatively new engineered wood material viable for the tall building construction. Currently, existing multi-story CLT buildings are mostly built in regions with low seismicity. Due to the lightweight nature of the wood material, CLT buildings have a relatively lower seismic force demand and great potential to achieve resilient performance in earthquakes. This study explores the potential use of an inter-story isolation system to achieve seismically resilient performance in platform tall CLT buildings. A generalized Displacement-based Direct Design (DDD) procedure was modified to identify key design parameters of the inter-story isolation system so that the building can achieve pre-selected displacement targets. The proposed design procedure was applied to a 12-story CLT building design example using Los Angeles, CA seismic hazard parameters. The as-designed building performance was validated numerically through nonlinear time history simulations. [ABSTRACT FROM AUTHOR]

Improving predictive relationships between strong ground motion and seismically induced damage in buildings is an important topic for seismic risk assessment. Spectral acceleration at a structure’s fundamental period S a ( T 1 ) has often been used as the indicator of the potential damage a given ground motion may induce on structural systems. However, such a scalar indicator (Damage Potential Indicator, DPI) captures only limited information about the ground motion time history and response spectrum shape. In a severely damaged state, the effective period of a structure will change, which makes the structure respond to other parts of the response spectrum. In this study, a new response spectrum-based DPI that contains an intensity component and a spectral shape component is proposed. The critical period range of the response spectrum that should be considered in spectral shape evaluation is determined using a circle rule for bilinear single-degree-of-freedom (SDOF) systems. The effectiveness of the newly proposed DPI is validated by comparing damage potential similarity using a database of ground motion records. [ABSTRACT FROM AUTHOR]

The ability to accurately quantify uncertainty in structural system seismic responses is a critical component of performance based earthquake engineering (PBEE). Currently, for nonlinear systems, this is achieved empirically using a large number of simulations with different excitation inputs (ground motion suites) and numerically randomized structural model samples. This study focused on one of the simplest nonlinear hysteretic systems, the bilinear single-degree-of-freedom (SDOF) oscillator, to develop a semi-closed-form solution for seismic response uncertainty as a function of 1) intensity-independent ground motion characteristics, 2) structural parameters, and 3) ground motion intensity level. This approach included the development of a parametric model for bilinear system IDA curves with intensity independent ground motion parameters and structural parameters. The accuracy of the proposed model was validated through nonlinear time history analysis (NLTHA) simulations. [ABSTRACT FROM AUTHOR]

• Events impacting tunnel functionality are identified based on duration & intensity. • Stochastic simulation model built to evaluate the downtime of tunnel infrastructure. • Separate modeling mechanism for event types. • Functionality loss quantified using a numeric metric. • Metric is used to compute resilience of road tunnels to disruptive events generated from the model. Given the importance of road tunnels in a transportation network, it is essential to quantitatively assess and predict tunnel functionality loss due to disruptive events. In this study, a stochastic event simulation model was developed to evaluate the resilience of tunnel infrastructure, quantified using a functionality metric as a function of loss in traffic capacity and its duration. The model consists of individual modules to account for disruptive events that cause tunnel closures. In this paper, the mechanism and probabilistic models used for each simulation module are presented. A simulation for Eisenhower tunnel, Colorado, was conducted using the proposed method as a validation case study. The results showed that the proposed model could simulate realistic tunnel operation status. While the validation was made for a specific tunnel, the model was designed to be applied to the resilience analysis of any road tunnel with defined design and operation parameters. [ABSTRACT FROM AUTHOR]

• The limits of traditional PBSD requirements for mass timber building is presented. • The process to combine traditional design and GA optimization is illustrated. • Two examples are designed and were shown to result in different designs. This paper presents a rational procedure to optimize design for mass timber rocking wall systems utilizing a genetic algorithm (GA) beyond typical displacement-based design metrics for wood buildings. Traditional displacement-based design is limited to simple displacement targets, with optimization techniques (GA), it is feasibly to consider more performance chrematistics (e.g. costs, serviceability, etc.). By formulating drift targets and other structural design limit states within an elimination step of the GA optimization process, the method proposed here optimizes rocking wall design with multiple criteria that factor much more than lateral displacement targets in the seismic analysis. This type of optimization is difficult to perform using traditional manual trial-and-error approaches. An existing simplified nonlinear time-history simulation model (validated through full-scale shake table test data) of a wood rocking wall is employed in this process. The design for an example building in Seattle with a six-story rocking wall is presented using the proposed procedure. The results revealed that the optimization of the mass timber rocking wall lateral system can be achieved in a reasonable time frame using the proposed method. Even though the same drift limits were applied, final designs produced by GA varied, depending on the other optimization objectives. This demonstrates how the seismic design of wood rocking wall systems could be readily improved with computerized optimization tools that factor in other aspects of the design including cost. [ABSTRACT FROM AUTHOR]

Cross-laminated timber (CLT) is a type of mass timber panel used in floor, wall, and roof assemblies. An important consideration in design and construction of timber buildings is moisture durability. This study characterized the hygrothermal performance of CLT panels with laboratory measurements at multiple scales, field measurements, and modeling. The CLT panels consisted of five layers, four with spruce-pine-fir lumber and one with Douglas-fir lumber. Laboratory characterization involved measurements on small specimens that included material from only one or two layers and large specimens that included all five layers of the CLT panel. Water absorption was measured with panel specimens partially immersed in water, and a new method was developed where panels were exposed to ponded water on the top surface. This configuration gave a higher rate of water uptake than the partial immersion test. The rate of drying was much slower when the wetted surface was covered with an impermeable membrane. Measured hygrothermal properties were implemented in a one-dimensional transient hygrothermal model. Simulation of water uptake indicated that vapor diffusion had a significant contribution in parallel with liquid transport. A simple approximation for liquid transport coefficients, with identical coefficients for suction and redistribution, was adequate for simulating panel-scale wetting and drying. Finally, hygrothermal simulation of a CLT roof assembly that had been monitored in a companion field study showed agreement in most cases within the sensor uncertainty. Although the hygrothermal properties are particular to the wood species and CLT panels investigated here, the modeling approach is broadly applicable. • Moisture and thermal properties of cross-laminated timber (CLT) were measured. • New method was developed for measuring water absorption on top of CLT panel. • Vapor diffusion contributed to water uptake in parallel with liquid transport. • 1-D transient hygrothermal model was validated with laboratory experiments. • Simulation of a CLT roof assembly compared well with field measurements. [ABSTRACT FROM AUTHOR]

Specimens testing and finite element analysis were conducted to investigate the fatigue performance of cope-hole details in welded integral joints of a steel truss bridge. A recommended nominal stress S-N curve of cope-hole details was obtained based on the evaluation of existing experimental results and comparison of different design specifications. The fatigue strength of the cope-hole details was evaluated via structural hot spot stress approach, which showed that the fatigue strength for the cope-hole details approaches that for FAT80. The effect of load type on local stress distribution was also identified by finite element parametric analysis. A simple equation was then proposed to estimate the stress concentration factor of cope-hole details in the tension member. [ABSTRACT FROM AUTHOR]

• A combination rule of wheel unloading extremes under random earthquake and track irregularity excitations was proposed from a probabilistic perspective view. • The seismic fragility analysis using the incremental dynamic analysis (IDA) was introduced into the vehicle-bridge interaction (VBI) system to simplify the probabilistic derailment assessment. • The accuracy of the IDA-based seismic fragility curve of the derailment was investigated for practical engineering application. With the rapid expansion of high-speed rail networks, the safety of vehicles against derailment on bridges during earthquakes has become a significant concern in bridge design. The vehicle's responses are the combined effect of earthquakes and track irregularities, both random processes. But few studies exist on the combination rule of derailment indexes from the two random excitations. In addition, the seismic fragility analysis commonly used in structural engineering was rarely seen in the derailment analysis. In this paper, the probability density evolution method (PDEM) was used to obtain the probability density function (PDF) of wheel unloading extremes by treating the earthquake and track irregularity as random processes. The combination rule of extremes of wheel unloading ratio from the two excitation sources was investigated by comparing the PDFs of combined results with direct simulation. It is shown that the extreme values of wheel unloading under earthquakes and track irregularities approximately satisfy the SRSS formula. In addition, the seismic fragility analysis using the incremental dynamic analysis (IDA) was introduced into the vehicle-bridge interaction (VBI) system to simplify the probabilistic derailment assessment. By comparing with the fragility curve from the PDEM (it can be seen as an accurate solution), the IDA-based seismic fragility curve estimated by twenty or more earthquake samples was found to have adequate accuracy for engineering application. [ABSTRACT FROM AUTHOR]

Abstract: In July 2009, a full-scale mid-rise light-frame wood apartment building was subjected to a series of earthquakes at the world’s largest shake table in Miki, Japan. The test program consisted of two major phases: the building tested in the first phase consisted of a single-story steel special moment frame (SMF) with six stories of wood on top, and the second phase consisted of locking down the steel story and testing the six-story light-frame wood building by itself. This paper focuses on the test results for the seven-story steel–wood building tested to earthquakes having return periods of 72 and 665 years. The objective of this phase of the test program was to investigate the performance of a mid-rise light-frame wood building with a first-story moment frame when subjected to a major earthquake, essentially providing a landmark data set to the seismic engineering research community. The building consisted of 225 square meters for retail space at the first story and 1350 square meters of multi-family residential living space with 23 apartment units above. The building was instrumented with just over 300 sensors and 50 LED optical tracking points to measure the component and global responses, respectively. In this paper the seven-story test specimen is described and the resulting seismic response and behavior is summarized. Detailed damage inspection was performed following each of these tests, and representative images are presented and discussed. The building was found to perform excellently, with very little damage following an event that was slightly larger (×1.16) than the design-level event for the city of Los Angeles, California. The peak global drift at roof level was 166 mm, and the peak inter-story drifts were approximately 1.3%. [Copyright &y& Elsevier]

Abstract: This paper presents an empirical seismic loss analysis procedure for woodframe buildings and examines how it can be utilized to provide input for the development of seismic performance objectives for woodframe buildings in terms of economic loss. This type of performance measure is more directly useful to building owners than qualitative performance levels such as “Life Safety” proposed in first generation performance-based seismic design documents. The procedure combines the PEER loss estimation methodology with the most up-to-date seismic numerical structural models for woodframe buildings and experimental data from full-scale shake table tests. The resulting loss estimates are quite reasonable when compared to observations from the 1994 Northridge, CA earthquake. The procedure is applied to two-story, single-family residential structures to estimate losses as a function of ground motion intensity and building design, and the results are discussed to illustrate how they can be used to help: (1) characterize estimated losses, (2) define performance objectives, and (3) guide design to meet those performance objectives. The study provides the first fully comprehensive application of the PEER methodology to woodframe buildings. [Copyright &y& Elsevier]

Vehicle-induced bridge vibration is an important design issue related to operational safety. The vehicle-bridge interaction (VBI) phenomenon has traditionally been simulated through time-history integration, which is powerful for research purposes but not convenient for every-day design. In this study, the accuracy of the moving load model (MLM) was improved by adding damping to the simply-supported bridges to account for the VBI effect. A semi-closed formula for this additional damping was derived based on the principle of equivalent energy dissipation. The proposed formula reveals the combination of vehicle and bridge parameters under which the maximum VBI effect occurs. The accuracy and robustness of the additional damping were checked by VBI numerical simulations covering a wide range of vehicle and bridge parameters. The proposed damping was shown to be more accurate than the damping specified by Eurocode 1 in predicting bridge vibrations. Using this damping formula, the response of simply-supported bridges can be easily obtained using the simple moving load model but can take into account the VBI effect. [ABSTRACT FROM AUTHOR]

This study is part of a research project examining fire risk in cross laminated timber (CLT) buildings. "Delamination", a major concern for CLT fire safety, can occur when the adhesive bondline fails in the panel before it chars which can lead to additional fuel for fire regrowth. Understanding the mechanical strength and stiffness of the adhesive bond under elevated temperature is one of the fundamental steps towards better understanding delamination. In this study, the material properties of wood and wood adhesive bonds are studied at various temperatures levels below the char temperature of wood (300 °C) to characterize the loss in strength and stiffness as a function of temperature. Four adhesives, three of which are commonly used in CLT production, were studied: two formulations made from polyurethane, one made from melamine formaldehyde, and one made from phenol-resorcinol formaldehyde. Tests were performed in a half-lap shear joint and compared against a specimen with identical geometry made from a solid piece of wood with no joint. The phenol-resorcinol formaldehyde joint had approximately the same shear strength as solid wood at all temperatures, whereas the other adhesives had noticeable reduction in strength at high temperatures. The method presented herein is unique among other CLT adhesive tests as it measures the performance of the adhesive under heat and load. [ABSTRACT FROM AUTHOR]

Highlights • First shake table test of platform-style CLT construction with continuous hold down rods. • Provides an opportunity assess stacked CLGT shear wall performance. • Quantify the behavior of nailed angle connectors on CLT stacked shear wall dynamic performance. • Assess the effect of transverse walls on CLT shear wall performance. Abstract Cross-laminated timber (CLT) manufacturing and construction has been steadily growing since its inception in Europe in the 1990s. In the US, the growth of the CLT adoption is inhibited by the lack of codified design provisions for CLT in high seismic regions. This led to a multi-year study conducted by Colorado State University to investigate suitable seismic design parameters of CLT shear wall systems. This paper presents the results from a series of shake-table tests featuring a full-scale two-story mass-timber building utilizing CLT Seismic Force Resisting Systems (SFRS). The building was designed using an R- factor equal to 4.0 under the equivalent lateral force procedure specifications of the ASCE 7-16 Standard. The test program included three phases with different wall configurations, reflecting different wall panel aspect ratios and the existence of transverse CLT walls. Test results indicate that the code-level life safety objective was achieved in all test configurations. The addition of transverse walls did not affect the ability of the panels to rock, and improved the performance of the building structural system. [ABSTRACT FROM AUTHOR]

In the US, codified seismic design procedure requires the use of seismic performance factors which are currently not available for CLT shear wall systems. The study presented herein focuses on the determination of seismic design factors for CLT shear walls in platform type construction using the FEMA P-695 process. Results from the study will be proposed for implementation in the seismic design codes in the US. The project approach is outlined and selected results of full-scale shear wall testing are presented and discussed. Archetype development, which is required as part of the FEMA P-695 process, is briefly explained with an example. Quasi-static cyclic tests were conducted on CLT shear walls to systematically investigate the effects of various parameters. The key aspect of these tests is that they systematically investigate each potential modelling attribute that is judged within the FEMA P-695 uncertainty quantification process. Boundary constraints and gravity loading were both found to have a beneficial effect on the wall performance, i.e. higher strength and deformation capacity. Higher aspect ratio panels (4:1) demonstrated lower stiffness and substantially larger deformation capacity compared to moderate aspect ratio panels (2:1). However, based on the test results there is likely a lower bound for aspect ratio (at 2:1) where it ceases to benefit deformation capacity of the wall. This is due to the transition of the wall behaviour from rocking to sliding. Phenomenological models were used in modelling CLT shear walls. Archetype selection and analysis procedure was demonstrated and nonlinear time history analysis was conducted using different wall configurations. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we examine issues related to the definition of seismic performance objectives at a regional scale. Specifically, we introduce a new regional seismic loss model for woodframe buildings and a building variant selection method that identifies a specific design for each building in a region based on stated performance objective policy guidelines. We then present full-scale applications of these methods for the city of Los Angeles, and examine how such analyses can inform a deliberative, public decision making process about what might constitute appropriate, achievable regional performance goals. The results suggest that for woodframe buildings, efforts to define performance policies at a regional scale should consider the empirical limits of what is reasonably achievable and how those vary by building type and location. Empirical and analytical analyses also indicate that targeting individual building loss performance does not necessarily guarantee the same level of regional loss performance. Further, at smaller target loss levels, the achieved regional loss may not be conservative in that the return period is smaller than in the targeted individual performance objective. While the empirical results presented apply only to woodframe buildings in Los Angeles, the general approach to examining performance policies at a regional scale could be applied to other structural types or regions. [Copyright &y& Elsevier]

Abstract: This paper highlights the development of a rapid visual screening (RVS) tool to quickly identify, inventory, and rank residential buildings that are potentially seismically hazardous, focusing on single-family, wood-frame dwellings with plan irregularity. The SAPWood software was used to perform a series of nonlinear time-history analyses for 480 representative models, covering different combinations of plan shapes, numbers of floors, base-rectangular areas, shape aspect ratio, area percentage cutoffs, window and door openings, and garage doors. The evolutionary parameter hysteresis model was used to represent the load–displacement relationship of structural panel-sheathed shear walls and a 10 parameter CUREE hysteresis model for gypsum wallboard sheathed walls. Ten pairs of ground motion time histories were used and scaled to four levels of spectral acceleration at 0.167, 0.5, 1.0, and 1.5g. An average seismic performance grade for each model was generated based on the predicted maximum shear wall drifts. Five seismic performance grades: 4, 3, 2, 1, and 0, are associated with the 1% immediate occupancy drift limit, 2% life safety limit, 3% collapse prevention limit, 10% drift, and exceeding 10% drift, respectively. The obtained average seismic performance grades were used to develop a new RVS tool that is applicable for checking the seismic performance of either existing or newly designed single-family, wood-frame dwellings. It examines the adequacy of the structure’s exterior shear walls to resist lateral forces resulting from ground motions, including torsional forces induced from plan irregularity. [Copyright &y& Elsevier]