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As inelastic design for wind is embraced by the engineering community, there is an increasing demand for computational tools that enable the investigation of the nonlinear behavior of wind-excited structures and subsequent development of performance criteria. To address this need, a probabilistic collapse assessment framework for steel structures is proposed in this paper. The framework is based on the integration of a high-fidelity fiber-based nonlinear structural modeling environment with a wind-tunnel-informed stochastic wind load model to perform nonlinear time history analysis. General uncertainty is propagated using a stratified sampling scheme enabling the efficient estimation of reliabilities associated with rare events. The adopted models for simulating high-fidelity nonlinear structural behavior were found, in general, to be adequate for capturing phenomena, including progressive yielding, buckling, and low-cycle fatigue, that are essential for wind induced collapse analysis. In particular, the adopted fatigue model was found to be capable of predicting damage and potential fiber/section fracture associated with non–fully reversing stress-strain cycles that are characteristic of wind loading. Through illustration on a 45-story archetype steel building, critical discussions on the types of observed collapse mechanisms, the difference between along-wind and across-wind nonlinear behavior, reliabilities associated with first yield, and collapse are presented. A probabilistic description of the residual and peak story drifts is also provided through development of fragility functions. [ABSTRACT FROM AUTHOR]

The article comments on the paper titled "Interactive Mechanical Model for Shear Strength of Deep Beams," by C.Y. Tang and K.H. Tan. The paper presented an interesting systematic study on the shear strength of deep beams. However, the experimental data, equations and references used in the study were not precise.

This paper presents an iterative automated method for optimizing structures with multiple deflection criteria and load cases. The method is based on the principle of virtual work. Discrete sections are selected for structures with fixed geometries. An optimal structure is one which meets all strength and deflection criteria using minimal material. Four case studies are considered in this paper. A simple portal frame is presented to show how the method works. A 60-story frame is optimized to demonstrate the effectiveness of the method for large structures. A warehouse designed by professional engineers is presented to show how the method can be used for structures subjected to complex loading conditions and deflection criteria. The automated method's solution is 4.5% lighter than the engineers'. Finally, a stepped cantilever is optimized and compared to results in literature. Material savings of up to 14.4% are realized. [ABSTRACT FROM AUTHOR]

Seismic design relies on inelastic deformations through hysteretic behavior. However, this translates into damage on structural elements, permanent system deformations following an earthquake, and possibly high cost for repairs. An alternative design approach, proposed in the past, is to concentrate damage on disposable and easy to repair structural elements (i.e., “structural fuses”), whereas the main structure is designed to remain elastic or with minor inelastic deformations. The implementation of the structural fuse concept into actual buildings would benefit from a systematic and simple design procedure. Such a general procedure is proposed here for designing new or retrofitted structures. The proposed structural fuse design procedure for multi-degree-of-freedom structures relies on results of a parametric study (presented in the paper), considering the behavior of nonlinear single degree of freedom systems subjected to synthetic ground motions. Nonlinear dynamic response is presented in dimensionless charts normalized with respect to key parameters. The proposed design procedure is illustrated as an example of application using Buckling-restrained braces as metallic structural fuses. This example is used in an experimental project (which is described in a companion paper) as a proof of concept to the developed design procedure. [ABSTRACT FROM AUTHOR]

This paper describes the development and results of a finite element parametric study of eccentrically braced frame links having hollow rectangular cross sections (i.e., tubular links). The parametric study involves over 200 combinations of geometries and properties and is divided into two parts. Part A considers a wide range of compactness ratios and link lengths to determine appropriate compactness ratio limits such that links with tubular cross sections can achieve desired rotation levels prior to significant strength degradation from local buckling. Part B of the study involves models developed with flange compactness ratios, web compactness ratios, and stiffener spacings near the proposed design limits from Part A, and also examines links having webs and flanges with different yield stresses (i.e., hybrid links). Results of the parametric study are also used to investigate the adequacy of a method for approximating link overstrength. A companion paper describes the experimental verification of the proposed design requirements. [ABSTRACT FROM AUTHOR]

This paper describes the buckling behavior of cold-formed steel equally lipped angle columns. The initial local imperfections, residual stresses, and corner material properties of the cold-formed steel angles have been measured experimentally and reported in this paper. An accurate finite element model was developed to carry out the buckling analysis. Both initial local and overall geometric imperfections have been incorporated in the model. The effect of residual stresses on the buckling behavior was investigated. The material nonlinearities of flat and corner portions of the angle sections were considered in the analysis. The finite element analysis was performed on equally lipped angles compressed between fixed ends for different column lengths, and column curves were obtained. The nonlinear finite element model was verified against recent experimental results. An extensive parametric study was carried out using the finite element model to study the effects of cross section geometries on the strength and behavior of lipped angle columns. The column strengths predicted by the finite element model were compared with the design strengths calculated using the North American Specification and Australian/New Zealand Standard for cold-formed steel structures. In addition, the results obtained from the finite element model were also compared with the design strengths obtained from proposed design rules. It is shown that the proposed design rules accurately predicted the column strengths for non-slender lipped angles and were quite conservative for slender lipped angles. [ABSTRACT FROM AUTHOR]

The paper addresses the design of angle section columns whose legs are slender and thus subject to local buckling in their ultimate limit state. For such slender angle sections, the local buckling mode is identical to the torsional mode and traditional design procedures become excessively conservative because they account for the torsional (local) buckling mode twice. The paper describes design methods for slender equal-leg angles which ignore torsion in determining the overall buckling stress and use recently presented effective width equations to accurately determine the bending capacity of angle sections, as required in the beam–column design approach. The shift in the effective centroid resulting from local buckling is determined from the actual stress distribution, as obtained using Stowell’s classical solution, rather than the effective cross section. The columns are assumed to be simply supported and thus allowed to rotate about their principal axes. [ABSTRACT FROM AUTHOR]

In this paper, different methods of lateral force distribution and design are described and compared with the results of experiments on a full-scale woodframe test house, and with a detailed three-dimensional analysis using a Finite Element (FE) model. The primary motive for this analysis and investigation is to provide the basic understanding required for the development of improved design procedure(s) for light-frame wood buildings subjected to lateral loads. Improved procedures for lateral load distribution should be analytically correct in their philosophy, and offer reasonable trade-offs between the uncertainties and omissions in the design process and simplicity for the end-user. In this paper, eight methods are used to predict the distribution of design wind forces to the walls of an example L-shaped single-story woodframe house, in a moderate hurricane prone environment. The results are compared and the differences in the predictions between the various methods are highlighted. Four of these methods are further compared against the results of physical experiments conducted on a full-scale test house. The FE model was generally the most accurate in predicting the experimentally measured load distribution, followed by the “plate method” and the “rigid beam method” described herein. [ABSTRACT FROM AUTHOR]

Several stages of performance need to be considered during the design of curved I-girders, including both the construction stage and the in-service conditions. Girder stability during the early stages of construction can be difficult to assess because the girders, at times, have little or no bracing present. One stage when there is no bracing present occurs when the girders are picked up from the ground or transport trucks by cranes and lifted into place. To better understand girder response during this critical stage, field studies were conducted on horizontally curved I-girders to measure rotations and stresses during the lifting process. This paper provides details of a semianalytical solution to predict the buckling and deformational responses of straight and curved girder segments during lifting. The deformations can be compared with rotational limits that were established to minimize problems with making connections to previously erected girder segments. The total rotational deformations of a horizontally curved girder result from two distinct components: (1) rigid-body rotation and (2) rotation caused by the girder cross-sectional twist owing to torsion from the girder's self-weight. A spreadsheet design tool, UT Lift, was developed to provide critical information for evaluating the rotational behavior of a horizontally curved I-girder during lifting and to estimate its lateral-torsional buckling capacity. An example of UT Lift's capabilities is presented along with background information on its development. Recommendations are given for safely lifting and erecting horizontally curved steel I-girders. [ABSTRACT FROM AUTHOR]

A LiteSteel beam (LSB) is a new cold-formed steel hollow flange channel beam produced by using a patented manufacturing process involving simultaneous cold-forming and dual electric resistance welding. It has the beneficial characteristics of torsionally rigid closed rectangular flanges combined with the economical fabrication processes from a single strip of high-strength steel. Although the LSB sections are commonly used as flexural members, no research has been conducted on the shear behavior of LSBs. Therefore, experimental and numerical studies were conducted to investigate the shear behavior and strength of LSBs. In this research, finite-element models of LSBs were developed to investigate their nonlinear shear behavior, including their buckling characteristics and ultimate shear strength. They were validated by comparing their results with available experimental results. The models provided full details of the shear buckling and strength characteristics of LSBs and showed the presence of considerable improvements to web shear buckling in LSBs and associated postbuckling strength. This paper presents the details of the finite-element models of LSBs and the results. Both the finite-element analysis (FEA) and experimental results showed that the current design rules in cold-formed steel codes are very conservative for the shear design of LSBs. The ultimate shear capacities from FEAs confirmed the accuracy of proposed shear strength equations for LSBs on the basis of the North American specification and direct strength method (DSM) design equations. Developed finite-element models were used to investigate the reduction to shear capacity of LSBs when full-height web side plates were not used or when only one web side plate was used, and these results are also presented in this paper. [ABSTRACT FROM AUTHOR]

In a companion paper, an alternative design approach was proposed to concentrate damage on disposable and easy to repair structural elements (i.e., “structural fuses”), while the main structure is designed to remain elastic or with minor inelastic deformations. To verify and validate the developed design procedure, an experimental project was conducted on the shaking table at the University at Buffalo, which consists of a three-story frame designed with buckling-restrained braces (BRBs) working as metallic structural fuses. This experimental project also assesses the replaceability of BRBs designed as sacrificeable and easy-to-repair members. These BRBs are connected to the frame by removable and eccentric gusset plate, especially designed to prevent performance problems observed in other experimental research. Design and behavior of this type of connection is also investigated here. Another objective of this test is to examine the use of seismic isolation devices to protect nonstructural components from severe floor vibrations in buildings designed per the structural fuse concept. The seismic isolation device consists of a bearing with a spherical ball rolling in conical steel plates, also called a ball-in-cone system. This type of seismic isolator was installed on the top floor of the frame model, and its response in terms of acceleration and displacement is investigated as part of this investigation. [ABSTRACT FROM AUTHOR]

This paper presents the results from an experimental pushover test on a one-third-scale model of a special inverted-V-braced steel frame with zipper struts. Zipper elements are vertical elements added at the intersections of the braces above the first floor and designed to carry upward the unbalanced loads resulting from buckling of the braces. As far as the writers know, this is the first test on such a configuration that has been suggested as an alternate to conventional braced frames in the American Institute of Steel Construction seismic specification for many years. The model was pushed to a target roof drift ratio of +3.58%, which was achieved without strength degradation and followed a trilinear backbone curve. The load was then reversed until the bottom story brace in tension fractured at a drift of -0.78%. After this fracture, the frame still carried about 37% of the maximum base shear. The zipper elements demonstrated their ability to activate buckling in all stories except the top one, redistributing the loads in the structure and minimizing strength losses. Two-dimensional and one three-dimensional frame models were analyzed and found to reproduce satisfactorily the experimental results up to the beginning of tearing in the tension brace. [ABSTRACT FROM AUTHOR]

This paper presents analytical approximate solutions for the geometrically nonlinear, large deformation postbuckling of a linear-elastic and hygrothermal beam with axially nonmovable pinned-pinned ends and subjected to a significant increase in swelling. The solution for the limiting case of a string is also obtained. Analytical approximations to large deformation of the beam are established by combining the Newton’s method with the method of harmonic balance. In contrast to the classical method of harmonic balance, the linearization is performed prior to proceeding with harmonic balancing, thus resulting in a set of linear algebraic equations instead of one of nonlinear algebraic equations. We are hence able to establish analytical approximate solutions. These approximate solutions show excellent agreement with the referenced solution obtained by the shooting method, and are valid for a small as well as a large angle of rotation at the end of the beam. [ABSTRACT FROM AUTHOR]

A simple numerical model to predict the dynamic characteristics, quasistatic pushover, and seismic response of woodframe buildings is presented. In this model the building structure is composed of two primary components: rigid horizontal diaphragms and nonlinear lateral load resisting shear wall elements. The actual three-dimensional building is degenerated into a two-dimensional planar model using zero-height shear wall spring elements connected between adjacent diaphragms or the foundation. The degrading strength and stiffness hysteretic behavior of each wood shear wall in the building can be characterized using an associated numerical model that predicts the walls load-displacement response under general quasistatic cyclic loading. In turn, in this model, the hysteretic behavior of each shear wall is represented by an equivalent nonlinear shear spring element. With this simple approach the response of the building is defined in terms of only three degrees of freedom per floor. This numerical model has been incorporated into the computer program SAWS (seismic analysis of woodframe structures). This paper discusses model formulation. In Part II, the predictive capabilities of this program are compared with recent shake table tests performed on a full-scale two-story woodframe house. [ABSTRACT FROM AUTHOR]

Even though a rigid floor diaphragm is a good assumption for seismic analysis of most buildings, several building configurations may exhibit significant flexibility in floor diaphragm. However, the issue of static seismic analysis of such buildings for torsional provisions of codes has not been addressed in the literature. Besides, the concept of center of rigidity needs to be formulated for buildings with flexible floor diaphragms. In this paper, the definition of center of rigidity for rigid floor diaphragm buildings has been extended to unsymmetrical buildings with flexible floors. A superposition-based analysis procedure is proposed to implement code-specified torsional provisions for buildings with flexible floor diaphragms. The procedure suggested considers amplification of static eccentricity as well as accidental eccentricity. The proposed approach is applicable to orthogonal as well as nonorthogonal unsymmetrical buildings and accounts for all possible definitions of center of rigidity. [ABSTRACT FROM AUTHOR]

Longitudinal cracks in wood beams of heavy timber structures are commonly seen and can impair the load-carrying capacity of such beams. This paper presents the experimental and numerical modeling results on 35 pieces of full-scale wood beams with saw kerfs that simulate lengthwise checks. The influences of the checks and self-tapping screws used for retrofitting purposes were identified based on the normalized load-carrying capacity of the tested beams. It was found that a longitudinal check (up to 2/3 of the beam span) may cause a resistance loss up to 46.2% compared to an unchecked beam, and the use of self-tapping screws may increase the resistance to no less than 86% of that of an unchecked beam. A three-dimensional (3D) finite-element method based model was developed and verified to further quantify the stress intensity factor at the check tip. Based on the modeling and test results, a simple formula was established for prediction of the stress intensity factor, considering the geometry of the checks and the contribution of the self-tapping screws. The generated formula was verified with good agreement and therefore can be used for determination of the shear resistance of checked wood beams and the required screw spacing for retrofitting purposes. [ABSTRACT FROM AUTHOR]

This paper attempts to enhance (1) the flexibility-corotational beam formulation for simulating highly geometrically nonlinear problems, and (2) the arc length method of integration to develop a robust and economical solution scheme for random quasi-static loading input. The existing flexibility-corotational formulation of a three dimensional beam is improved by (1) updating the rotation matrices by using the quaternions, and (2) proposing novel methods for tracking the displacement compatibility. Further, the cylindrical arc length method is modified by (1) introducing capabilities for handling random quasi-static loading, and (2) proposing automatic adjustment of the arc length. By using these developments several classical geometric nonlinearity problems are solved and path independency for buckling and post-buckling path with the random quasi-static loading is verified. The proposed variation in the arc length solution scheme is also shown to be better than the implementation of the arc length method in the state of the art commercial software. [ABSTRACT FROM AUTHOR]

This paper presents a formal optimization methodology for the design of seismic retrofitting of three-dimensional irregular buildings. The damping coefficients of viscous dampers potentially allocated in given feasible locations as well as the stiffness of their supporting braces are adopted as design variables. The objective function minimizes a cost function of the dampers while constraints are added to limit various responses of interest to allowable values under a filtered white noise excitation (e.g., interstory drift at each location separately, total acceleration at each location separately, force of each damper, stress in each supporting brace, force/forces of each structural member, base shear, overturning moment at the base, side constraints on dampers' forces and braces' cross sections, etc.). A first-order optimization method is adopted for that purpose. The constraints on various normalized responses are condensed to a single constraint on their maximum value and the gradient required is efficiently derived analytically using the adjoint analytical method. Thus, a computational effort at the order of a single additional analysis is required for the evaluation of the gradient of the constraint regardless of the number of design variables considered or responses to be constrained. This efficient scheme enables a study on the effect of limiting the brace size with and without a limit on its stresses. [ABSTRACT FROM AUTHOR]

The properties of special concentrically braced frames (SCBFs) enable them to be designed to meet performance-based seismic design (PBSD) criteria. SCBFs have large stiffness and strength to meet serviceability performance states. Life-safety and collapse-prevention PBSD limit states are controlled by inelastic postbuckling and tensile yield deformation of the brace. In SCBF construction, the braces are connected to the frame using gusset plates. Inelastic deformation of the brace places severe inelastic demands on gusset-plate connections. To improve the understanding and design of the seismic performance of SCBF connections, a coordinated analytical and experimental research study was undertaken. This paper describes the analytical component and includes a brief description of the experimental results, which were used in the development and validation of the model. The validated model was used to evaluate the inelastic performance of structural elements and to determine the frame ductility and concentration of plastic strains at potential locations of member or weld tearing or fracture. Detailed comparisons between experimental observations and computed results show that the analyses provided good correlation to actual behavior. The results were used to develop a methodology to predict tearing or cracking of key elements in the frame. [ABSTRACT FROM AUTHOR]

I-shaped steel girders with tubular flanges have been studied for application in highway bridges because of their large lateral torsional buckling (LTB) strength relative to conventional I-shaped steel plate girders. This paper discusses the LTB strength of tubular flange girders, focusing on concrete-filled tubular flange girders (CFTFGs) where the concrete-filled tube is the compression flange. Using finite-element (FE) models of CFTFGs, a parametric study was conducted to investigate the influence of girder geometry and material strength on the LTB strength. Design flexural strength formulas, considering LTB, for construction conditions and for ultimate strength in the final constructed condition, were developed based on the results of the parametric study. These formulas estimate the LTB strength of CFTFGs that are perfectly braced laterally and torsionally at brace points. A similar FE study of conventional I-girders was conducted and the results are compared with those of CFTFGs. [ABSTRACT FROM AUTHOR]

Empirical estimates of the fundamental frequency of tall buildings vary inversely with their height, a dependency not exhibited by the various familiar models of beam behavior. This paper examines and explains this apparent discrepancy by analyzing the consequences of using two models to estimate such natural frequencies: A two-beam model that couples the bending of a classical cantilever to that of a shear beam by imposing a displacement constraint; and a Timoshenko beam in which the Euler–Bernoulli beam model is extended by adding a shear-displacement term to the classical bending deflection. A comparison of the two beam models suggests that the Timoshenko model is appropriate for describing the behavior of shear-wall buildings, while the coupled two-beam model is appropriate for shear-wall–frame (e.g., tube-and-core) buildings, and that the coupled-beam model comes much closer to replicating the parametric dependence of building frequency on height. [ABSTRACT FROM AUTHOR]

Ductile end cross frames have been proposed in the past as a seismic design and retrofit strategy for steel plate girder bridges. In this paper it is shown that with good connection details, single angles are able to undergo large cyclic deformations in excess of 6% average axial strain before failure occurs. Large-scale shake table experiments were performed on a straight steel I-girder bridge model to evaluate the performance of a superstructure with ductile end cross frames using single angle X braces. The cross frames exhibited no apparent overall strength degradation, but also a comparatively low postyield stiffness, allowing the cross frames to act as effective structural fuses. The measured base shear was 61% of the elastic base shear in response to 2.0 times the El Centro earthquake at an average drift of 3.4%. Large girder drifts were achieved without distress in the deck slab by removing selected studs between the slab and top flange of the girders at the end cross frame locations, with axial deformations in the angles well below their deformation capacity based on component experiments. [ABSTRACT FROM AUTHOR]

This paper presents test results on eight reduced beam section (RBS) steel moment connections. The testing program addressed web connection type (bolted versus welded) and panel zone (PZ) strength as the key variables. Specimens with medium PZ strength were designed to promote energy dissipation from both PZ and RBS regions such that expensive doubler plates were not needed. Both strong and medium PZ specimens with a welded web connection were able to provide satisfactory connection rotation capacity for special moment-resisting frames. However, specimens with a bolted web connection performed poorly due to premature brittle fracture of the beam flange at the weld access hole. A plausible explanation for the higher incidence of base metal fracture in bolted web specimens was presented based on the measured strain data. Test results from this study and by others showed that panel zones could easily develop a plastic rotation of 0.01 rad without causing distress to the beam flange groove welds. At this deformation level, the amount of beam distortion (i.e., buckling) was about one half that developed in strong PZ specimens. A criterion for a balanced PZ strength that improves the plastic rotation capacity while reducing the amount of beam buckling is proposed. [ABSTRACT FROM AUTHOR]

This paper experimentally investigates the cyclic inelastic performance of concentrically braced frames with and without cold formed steel stud (CFSS) infills designed to laterally restrain braces and delay their buckling. Specimens have either diagonal tube or solid bar braces with and without CFSS and U brackets providing out-of-plane and in-plane buckling restraint. Behavioral characteristics of the specimens are quantified with an emphasis on hysteretic energy dissipation. Experimental results show that, at the same ductility levels, the cumulative energy dissipation of braced frames can be significantly increased when CFSS members are used to laterally restrain the braces against buckling. However, when tubular cross sections are used for braces, local buckling led to a reduced fracture life compared to the case without CFSS members. CFSS members appear to be relatively more effective when solid bar braces having large slenderness (tension-only braces) are used, since the difference between dissipated energies obtained with and without studs is substantial. [ABSTRACT FROM AUTHOR]

Longitudinal stiffening increases the ultimate strength of plate girder webs subjected to compressive edge load, commonly referred to as patch loading. This increase in most design codes has been disregarded. Therefore, this paper presents the background of three design models developed to quantify this increase in ultimate strength. The first model is based on the regression analysis of experimental results carried out around the world. The second is based on a modification of the yield line method used for unstiffened plate girders. Finally, the third one is based on a buckling curve approach. The third model is the most complete, accounting for stiffener properties, and also provides the best agreement with test results. [ABSTRACT FROM AUTHOR]

Presents information on a study which developed an inverse design method for frames by means of an inverse formulation including frame stability effects. Inverse design problem for specified bending strains; Formulation of the hybrid-inverse design problem; Inverse design of frame consisting of centrally compressed-columns; Conclusions.

The article replies to criticism on the authors' paper titled "Interactive Mechanical Model for Shear Strength of Deep Beams." The authors provided explanations for the various points raised by the discusser. It was clarified, among others, that the coefficient 0.5 in equation 15 is not a fitting parameter.

Introduces the topics and issues contained in the July 2005 issue of the "Journal of Structural Engineering." Evaluation of drift demands for the seismic performance assessment of frames; Establishment of the relationship between drift demand and a seismic intensity measure; Propositions for a simple procedure to establish drift estimates in frame buildings subjected to near-fault ground motions.

Presents the results of static and cyclic lateral load tests on wooden frames that constitute an ancient Korean house. Test method; Test results; Simulation of nonlinear behavior; Conclusion.

This paper describes a test program conducted on the behavior of cold-formed, compact square hollow section beam-columns. The tests were conducted in a purpose built test rig capable of applying load and moment in a constant ratio. The test specimens were pin-ended specimens loaded, with varying load/moment ratios, at two different ratios of end moment. The results of the tests were closely simulated using a finite-element program, thereby validating its use in predicting cold-formed tubular beam-column behavior. The finite-element program was then used to find the maximum load and moment capacity, for the section tested, at varying ratios of end moment, from which the corresponding maximum second-order elastic moments were calculated. The results of this numerical investigation are compared with the relevant interaction design rules from the 1990 Australian standard AS4100 and the 1986 American Institute of Steel Construction (AISC) load and resistance factor design (LFRD) specification. [ABSTRACT FROM AUTHOR]

The current specifications for fatigue design of hollow structural section (HSS) connections are both outdated, and, in view of recent research results fairly inaccurate. Analyses of a large number of connections have been carried out, incorporating results from other researchers. The result is this paper, which contains an outline for improved fatigue design guidelines for HSS structures that are welded directly together without the use of additional stiffeners. To clarify the use of these guidelines and show the difference between the proposed and existing design methods, three HSS connections are analyzed with existing design guidelines as well as with the proposed guidelines. [ABSTRACT FROM AUTHOR]

Significant evidence based on experimental research exists to give designers confidence in the use of theoretical equations to evaluate the pullout strength of threaded steel rods glued into timber. However, the mechanism of load transfer through a timber frame moment joint utilizing glued-in steel rods requires more than simply understanding the tension performance of a glued-in rod. A method of evaluating joint strength for moment and axial forces based on traditional mechanics theory adapted for use with timber is presented. Formulas were derived from first principles for joint configurations, with extended columns or with extended beams and with various types of construction (i.e., with rods fully glued along their entire length or only glued in one of the two members connected and then tensioned). The design method also considers the effects of time-dependent deformation in timber at bearing interfaces and the effects of stress concentrations imposed by the steel rods on the timber. Some open questions that deserve further investigations are highlighted, as well as some possible details to optimize joint performance while retaining ease of assembly. The approach provides a methodology for joint design that has been successfully used in many projects. [ABSTRACT FROM AUTHOR]

Tubular-section members are commonly used as seismic-resistant braces because they have a higher moment of inertia than open cross sections of equivalent area. However, the cumulative cyclic deformation capacity of tubular sections after buckling is smaller than that of open sections, such as H-shaped sections, because fracture is initiated by local buckling of circular tubular sections. To evaluate the seismic performance of such diagonal braces, it is essential to predict the cumulative cyclic deformation capacity of these braces before any fracturing. In this study, the cumulative cyclic deformation capacity of circular tube braces under local buckling was assessed by performing cyclic loading tests for a range of slenderness and diameter-to-thickness ratios. The mechanism of strain concentration in the tubular braces was studied in various types of analysis, and a method is proposed for assessing the cumulative deformation capacity before fracture based on the entire axial deformation of the braces. [ABSTRACT FROM AUTHOR]

Existing welded steel moment frames are designed to tolerate substantial yielding and plastic rotation under earthquake loads. This sacrificial design approach can lead to permanent, and often irreparable damage when interstory drifts exceed 2%. The experimental seismic performance of a 50% full-scale damage avoidance designed structural steel beam-column connection is presented. The beam-column joint region consists of a top flange-hung beam connected to the column by an angle bracket. High-force-to-volume (HF2V) devices are attached from the column to the beam to provide joint rigidity and energy dissipation as the joint opens and closes. The HF2V devices are connected either below the beam flange or concealed above the beam’s lower flange. Reversed cyclic lateral load tests are conducted with drift amplitudes up to 4%. No damage is observed in the principal beam and column structural elements. The need for stiff device connections to achieve optimal device performance is demonstrated, and potential design solutions presented. Stable hysteresis and repeatable energy dissipation for a large number of cycles up to the 4% drift level is observed. It is concluded that superior and repeatable energy dissipation without damage can be achieved for every dynamic motion cycle, in contrast to conventional sacrificially designed welded moment frame connections. [ABSTRACT FROM AUTHOR]

Seismic performance requirements for beam-column joints of earthquake-resistant reinforced concrete (RC) frames are discussed, and the experimental data of RC joints under cyclic loading collected from the literature are analyzed. It is observed that joint shear failure under cyclic loading is characterized by significant inelastic joint shear deformation. Joint shear strength should thus be formulated by limiting the influence of joint shear deformation on the seismic performance of RC frames. It is noticed that joint transverse reinforcement does not have significant influence on joint shear deformation and bond deterioration in the joints but may have significant influence on joint axial capacity under cyclic loading. Hence, the requirement for joint transverse reinforcement may be formulated by keeping the joint axial capacity not lower than the column axial capacity under seismic action. The influence of bond deterioration in joints on the seismic performance of RC frames and the anchorage requirement for beam reinforcement in joints are analyzed and discussed. [ABSTRACT FROM AUTHOR]

The overall goal of this study is to gain an insight into the load sharing aspect between oriented strand board (OSB) and gypsum wall board (GWB) in shear wall assembly during racking load. Sixteen standard 2,440×2,440 mm walls were tested monotonically, in total, out of which 11 (Type A) were sheathed on both sides (OSB on one side and GWB on the other), while five walls were tested without GWB (Type B). Digital image correlation (DIC) was used for data acquisition and analysis which is a full-field, noncontact technique for measurement of displacements and strains. The system returns full-field three-dimensional displacement and strain data measured over the visible specimen surfaces. Overall, these tests suggest that initially during loading of a wall the load is shared between OSB and GWB. However, the proportion of load sharing is not known. As GWB fails first at about 60% of ultimate load capacity of the wall, the load shifts to the OSB panel which resists it until the failure of the wall. The tests also revealed that the load path in wall Types A and B is different and so is the failure pattern. Strains were locally concentrated around the fasteners, while the strains in the field of the panel were below the detection limit of DIC system. [ABSTRACT FROM AUTHOR]

Structural control using energy dissipater devices is emerging as a heavily researched strategy in earthquake engineering. Among several control systems, semiactive control is usually possible and efficient. In this research, a semiactive energy dissipating bracing system based on a viscous damper is proposed. In the conventional bracing systems, it is assumed that the braces can buckle under compression. Therefore, a semiactive on-off brace strategy is implemented to improve the conventional brace performance. Further, an energy absorbing mechanism is implemented. In the proposed system, the buckling of the member is prevented by implementing a one-way valve device. The permanent story drifts at the end of excitations are negligible. In this mechanism, any actuator and/or large power supply are not needed, instead, just battery-size power supplies to switch the one-way valve mechanical system on or off. The developed mechanism is composed of a viscous damper, a length correction control system, and a normal wind bracing on each floor. Despite the fact that this system does not get control command from the outside, it is called a semiactive control system. The hysteresis loop of the braces is almost similar to ductile tensile steel members. Therefore, the system is full capacity design. Nonlinear dynamic analysis of the system has been carried out and structural behavior has been investigated. In addition, damage indices are determined in order to compare the viscous tensile bracing system with the conventional bracing systems. [ABSTRACT FROM AUTHOR]

An experimental study was conducted to investigate whether existing industry design procedures for tight-fitting metal plate connector truss joints can be applied to the design of joints made with round-end webs. Four joint configurations were tested with a range of connector-plate sizes: 45° with web in tension, 45–45° with one web in compression and the other in tension, 45–90° with the 45° web in compression and the 90° web in tension, and 45° with the web under compression. In total, 87 tight-fitting and 171 round-end joints were tested. As expected the tight-fitting joints were stronger and stiffer than round-end joints. Both the shear strength of the metal plate connector and the teeth pullout strength were smaller in the round-end joints than in the tight-fitting joints. The line contacts between the round-end webs in compression produced greater crushing of the wood, causing buckling of the connector plates, and reducing the ultimate loads on these joints. Design guidelines are suggested for round-end joints. [ABSTRACT FROM AUTHOR]

The quasi-plastic-hinge approach proposed by Attalla et al. in 1994 for material nonlinear analysis is formulated using the total form expressions, which is generally computationally inefficient as numerical integrations and finite-difference schemes are required to obtain the elastic-plastic flexibility coefficients. To overcome the above drawback, the quasi-plastic-hinge approach is formulated in an incremental form for beams with uniform cross sections, by which the elastic-plastic flexibility coefficients are explicitly given. The procedure is directly extended to nonuniform beams through use of different moment-curvature relations for the two ends of the beam, or indirectly through subdivision of the beam into a number of inner segments. The elastic-plastic flexibility coefficients derived for both cases are also explicitly given. For comparison, three steel frames composed of nonuniform cross sections are studied, from which the accuracy of the proposed approaches for treating frames with uniform and nonuniform cross sections is verified. [ABSTRACT FROM AUTHOR]

Reversed cyclic loading tests of eight prestressed and two nonprestressed concrete exterior beam-column joint assemblies that failed inside the joint cores were conducted. The test results revealed no significant difference in the maximum story shear force between the prestressed and nonprestressed concrete test units although the horizontal input shear forces of the joint cores at the maximum story shear forces of the prestressed concrete units (calculated based on the column shear force and the forces in the reinforcing and the prestressing steels) were greater than those of the nonprestressed concrete units. On the basis of this result, the writers have concluded that prestressing force does not play a major role on the ultimate shear strength of beam-column joint cores. In addition, the design shear force acting on a beam-column joint core should be determined using the average shear force calculated from the bending moment at the beam-column interfaces, not by the horizontal input shear force. These conclusions led the writers to develop design equations for estimating design shear forces and ultimate shear capacities of prestressed concrete interior and corner joints. The equations were compared with test data on 51 beam-column joint assemblies that failed in shear in the joint cores. The test results agreed well with the estimations. [ABSTRACT FROM AUTHOR]

An analytical study was conducted on the cyclic loading behavior of beams in steel moment frames. Lateral–torsional buckling and local buckling were explicitly considered in the analysis. Beam cross-sectional dimensions were varied to represent a wide range of rolled wide flange shapes. The unbraced length of the beams corresponded to slenderness ratios about the weak axis ranging between 60 and 100. Based on the analyses, flange and web width-thickness limits were established that would permit the beam to achieve various target rotation capacities. These limits are presented in terms of limit curves which plot the flange width-thickness ratio against the web width-thickness ratio. The limit curves clearly show strong flange–web interaction. Different limit curves were developed for a range of target rotation angles, weak axis slenderness ratios, and residual strength levels. Postbuckling behavior and strength degradation mechanism were studied. The results of the analyses are compared against current building code requirements for beam stability in seismic steel moment frames, and the adequacy of the current code requirements are evaluated. [ABSTRACT FROM AUTHOR]

A new method via inverse problem formulation including frame stability (P-δ and P-Δ effects) is presented for state-specified design of an arbitrary planar elastic frame. The well-known governing equations for second-order analysis with respect to unknown displacements for a set of prescribed member stiffnesses of a frame are here regarded as those with respect to unknown member stiffnesses for a set of prescribed member-end strains and displacements. A method of sequential mapping for such a “direct design”problem is generalized for a hybrid inverse problem of an arbitrary plane frame such that a combined set of unknown member stiffnesses and unknown member-end strains (or displacements) is to be found for a set of prescribed member-end strains (or displacements) and prescribed member stiffnesses. The concept of “state-design vector” is shown to be useful for such a general problem of hybrid-inverse mapping. A general design program has been developed on the basis of the proposed algorithm on the first-order equations. Four design examples not only demonstrate the program performance but also disclose P-δ and P-Δ effects on the design. A guideline is described for practical application in compliance with an allowable stress design code. [ABSTRACT FROM AUTHOR]

A methodology for semiactive control of building frames using multiple semiactive hydraulic dampers (SHDs) driven by fuzzy controllers is presented. The SHDs are installed in combination with steel bracings and are placed at different floor levels. The fuzzy controller is designed for the bottom-most SHD. Other controllers are assumed to provide control command for the variable damping coefficient of an SHD in certain proportion to that obtained for the bottom-most controller. Different proportions giving different distributions of the semiactive control force along the height of the frame are tried in order to arrive at the best distribution for obtaining the maximum control of a response quantity of interest. The methodology is developed in the MATLAB environment using the SIMULINK and FUZZY tool boxes. As an illustrative example, a five-storied steel frame is selected from the literature. The control of the responses of the frame under the El Centro earthquake record is obtained for a specified set of the frame, steel bracings, and SHD properties. An extensive parametric study is conducted to investigate the effectiveness of the control scheme under variation of the important parameters. The control strategy with the optimum values of parameters designed for the El Centro earthquake is tested for three synthetically generated earthquakes. The results of the study show that an efficient semiactive control strategy can be developed using a fuzzy rule base. Further, optimum combinations of parameters for maximum control are different for different response quantities of interest. [ABSTRACT FROM AUTHOR]

An analytical study was conducted to investigate the influence of the flange width–thickness ratio on the rotation capacity of links in eccentrically braced frames. Finite element models, verified using experimental data, were used to investigate the performance of 112 links. Models simulated strength degradation associated with flange and web local buckling that may occur during cyclic loading. The models provided data for short, intermediate, and long links with a range of flange width–thickness ratios. Results indicate that a relaxation of the flange width–thickness ratio requirement in current AISC seismic design provisions is justified. It was also found, however, that the provisions specify nonconservative design rotations for some intermediate links. This is shown to be related to web stiffener spacing and not the flange width–thickness ratio. [ABSTRACT FROM AUTHOR]

A practical model has been developed to predict, for a given level of lateral deformation, the likelihood that longitudinal bars in a reinforced concrete column will have begun to buckle. Three relationships linking plastic rotation, drift ratio, and displacement ductility with the onset of bar buckling were derived based on the results of plastic-hinge analysis, moment-curvature analysis, and the expected influence of the confinement reinforcement. These relationships, which account for the effective confinement ratio, axial-load ratio, aspect ratio, and longitudinal bar diameter, were calibrated using observations of bar buckling from cyclic tests of 62 rectangular-reinforced and 42 spiral-reinforced concrete columns. A version of the drift ratio relationship is proposed for earthquake engineering applications. The ratios of the measured displacements at bar buckling to the displacements calculated with the proposed model had a mean of 1.01 and a coefficient of variation of 25% for rectangular-reinforced concrete columns. The corresponding mean and coefficient of variation for spiral-reinforced columns were 0.97 and 24%, respectively. [ABSTRACT FROM AUTHOR]

A simple formula is developed to estimate the separation distance required between single-story steel frames and firewalls so that during an uncontrolled fire the frame can expand without contacting and damaging the wall. Detailed analysis shows that the frames reach their maximum lateral displacement at the birth of plastic hinges in the girders. The hinges allow the girders to sag excessively, pulling inward on the columns and causing the frame to collapse away from firewalls. The simple method presented uses the frame geometry, member cross sections, loads, and the temperature-dependent steel properties to predict the steel temperature at which the plastic hinges form. The formula uses this temperature and the equilibrium of the deformed frame to calculate the minimum acceptable clearance. The fire is assumed stationary and fully developed. The exposed portions of the structure are assumed totally enveloped by the hot gas. The method includes the column resistance to thermal expansion and the plastic deformations that originate from the second-order effects due to the axial loads in columns acting on the deformed frame. The approach lends itself to spreadsheet calculations for fast design decisions and is accurate, which is demonstrated by good agreement with experimentally validated finite element results. [ABSTRACT FROM AUTHOR]