Search

Abstract: A two-dimensional beam–column joint element for simulating steel beam-to-concrete filled steel tube (CFT) column connections is proposed. This joint element is composed of a panel zone element and springs to model the different deformation components in the beam–joint/column–joint region. The development of the spring components' strength and stiffness and its implementation in OpenSEES are described. Analytical models of steel beam-to-CFT column connections are created in OpenSEES and the results are compared to experimental data from test on individual connections, including connections with through diaphragms, internal diaphragms and external diaphragms. In general, very good correspondence is found between the analysis and test results. The reasons for the differences observed between some models and test results are probably related to friction, rotational restraints and initial deformations in the test specimens. Compared to existing joint elements, the proposed joint element provides a general approach to simulate various composite connection types while the translational springs provide more freedom to simulate connections with unsymmetrical beam sections or slab effects. The element is flexible in accounting for plastic hinge locations and simple to implement for a practicing structural engineer. [Copyright &y& Elsevier]

Composite steel-concrete columns and beam-columns have been shown to provide superior performance when the intrinsic synergistic characteristics of concrete and steel are properly exploited. However, limited test data are available to justify the structural system response factors and comprehensive design equations in current design specifications. This research, through the testing of 18 full-scale, slender concrete-filled steel tube (CFT) beam-columns, addresses these needs by providing comprehensive data to calibrate advanced computational models and assess design equations. The CFT specimens were subjected to complex load protocols that included pure compression, uniaxial and biaxial bending combined with compression, pure torsion, and torsion combined with compression. The results for the pure compression tests reported in this paper indicate that current AISC design provisions provide an accurate estimation of column capacity for both strength and stiffness. The experimental loading response was also contrasted with column curves obtained from advanced, nonlinear fiber analysis models. The experimental and computational column curves are strongly correlated in the elastic critical load range, but showed some differences in the inelastic buckling load range. These differences are attributed to the higher concrete strength assumed in the computational analysis because of the confinement effect of the steel tube; this strength is underpredicted in current design specifications. [ABSTRACT FROM AUTHOR]

Abstract: The mechanical models used to simulate the complete behavior of full-scale bolted T-stub connections under cyclic loads are mainly treated in this paper. These mechanical models are composed of individual T-stub components modeled as nonlinear spring elements in order to reliably reproduce their various response mechanisms interacting with one another in the connection. The hysteresis behaviors of the T-stub components including bolt/flange uplift, stem elongation, and relative slip deformation combined with bolt bearing are simulated by the multi-linear cyclic stiffness models characterized from their actual force–deformation response mechanisms each. The nonlinear component springs, which contain these idealized stiffness properties, are implemented into the user joint element produced based on the mechanical model so as to numerically generate the complete behavior of the full-scale connections with considerable accuracy. The analytical predictions performed on the joint element are evaluated against the experimental tests with respect to stiffness, strength, and deformation. Thus, the adequacy of the proposed modeling approach is verified through comparisons between analytical predictions and experimental test results. Finally, it can be shown that the mechanical model proposed in this study has the satisfactory potential to predict the response of the T-stub components as well as the behavior of the T-stub connections through analytical studies. [Copyright &y& Elsevier]

Abstract: This paper deals with mechanical models which make it possible to reliably simulate the complete moment–rotation curves in the full-scale T-stub connections subjected to cyclic loads. The behavior of these bolted connections becomes complex because the various response mechanisms of individual connection components interact with one another and have influence on the overall rotational stiffness of the connection. Accordingly, the mechanical joint models are made up of individual T-stub components modeled as nonlinear springs. The behaviors of component members including tension bolt uplift, bending of the T-stub flange, elongation of the T-stem, relative slip deformation, and bearing deformation are reproduced by the multi-nonlinear stiffness models obtained from their force-deformation response mechanisms. These stiffness properties should be assigned into the component springs implemented into the joint element so as to numerically generate the behavior of full-scale connections with considerable accuracy. Thus, this part (Part I) intends to focus on describing the stiffness models, which are based on the basic component spring theory, in an effort to provide insight into the behavior, failure modes, and ductility of T-stub components in the connection. [Copyright &y& Elsevier]

Abstract: As the trend towards developing performance-based design specifications for the seismic design of structures gains momentum, it is clear that very little is known about the performance of light industrial structures under large lateral loads. Among the main outstanding issues related to the seismic design of these structures are (1) the determination of appropriate response modification factors , (2) the establishment of drift limits to avoid damage of structural and nonstructural components, and (3) clarification of the role that the roof diaphragm plays on the seismic behavior of light-weight roof structures. This study attempts to elucidate some of those issues for a particular class of light-weight industrial structures, those composed of one-story, weak column–strong beam joist girder frames. Two types of analysis models were developed for the nonlinear dynamic analyses of these structures. The first is a simplified 2-D analysis model, using SAP2000 and the second is a complex 3-D analysis model, using ABAQUS. Nonlinear time history analyses were performed for sites in Los Angeles (CA), Boston (MA), and Memphis (TN). The accuracy of the simplified 2-D model was verified by comparison with the results from the 3-D model. The results indicate that the behavior of these structures is almost always in the elastic range, and that substantial roof bracing should be installed for this type of structure, to prevent excessive drifts in the weak direction. When two horizontal components of excitations were applied concurrently to check the effect of torsion of the frame, it was found that torsional effects were negligible for structures regular in plan, and that a 2-D model can provide reasonable analysis results. Column base fixity effects on the dynamic behavior were also investigated and it was determined that column base fixity should be considered, to obtain more accurate dynamic behavior of the steel joist girder structures. [Copyright &y& Elsevier]

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]

Abstract: This paper proposes a design methodology for zipper-braced frames aimed at achieving ductile behavior. Three zipper-braced models were designed on the basis of the proposed design procedure to carry the same masses as the 3-, 9-, 20-story SAC model buildings with moment-resisting frames designed for the Los Angeles area. Pushover analyses of the models were performed to estimate the overstrength, inelastic strength and deformation capacities for the entire structures, and assess the sequence of yielding and buckling in the members. The performance of the models was also evaluated using nonlinear dynamic analyses under an ensemble of 2%-in-50-year pulse-type near-fault ground motions. The analyses indicate that the design procedure produces safe designs, with the design becoming more conservative as the number of stories increases. The distribution of interstory drifts demonstrates the efficiency of the zipper struts in achieving uniform damage over the height of the structure, and generally satisfies allowable interstory drift ratio limits. [Copyright &y& Elsevier]

The wind moment frame (WMF) method has been and continues to be widely utilized in the central and eastern United States, resulting in a very large population of structures having been designed without a rigorous analysis with respect to lateral loads. The primary objectives of this paper are to determine whether moment-resisting frames designed by the WMF method are adequate to handle the increased demand on lateral resistance made by modern seismic codes, and to evaluate and compare the seismic performance of existing and new moment-resisting steel frames with partially restrained (PR) connections. Three prototype frames were designed and analyzed utilizing synthetic ground motions for the Mid-America region. The seismic performance of these PR frames was evaluated in accordance with FEMA 273/356 criteria. In addition, studies were conducted on the confidence level of the performance results to take into account the uncertainties and randomness inevitably involved. This analysis and evaluation found that all PR frames designed in this study satisfied the selected performance objective with 99% confidence level for the global performance limit. Thus, the seismic performance of the PR frames in the Mid-America region will be satisfactory even under large ground motions. [ABSTRACT FROM AUTHOR]

Partially restrained connections and their interaction with the floor slab have received recent attention due to numerous failures of welded steel moment frames during the 1994 Northridge and 1995 Kobe earthquakes. After the earthquakes, it was apparent that the “simple” connections, including the slab, served as a “backup” structural system after the full moment connections failed. These connections significantly influenced the behavior of the lateral load resisting system. This paper reports on the results of a unique, full-scale bidirectional test on a composite connection. The connection behaved very well up to a uniaxial drift of about 2%. After that drift level, composite action began to deteriorate and the connection strength and stiffness declined. The results indicate that two previously unreported failure modes may need to be considered in the design of composite buildings if large cyclic bidirectional forces are present. One is a “punch through” of the column web due to the force transfer from the “pinned” side of the connection. The other is the formation of a concrete wedge as a result of the large bearing forces between the slab and steel column flange. As a result of this observation, a suggestion that the full depth of the slab be maintained for a region 150 mm (6 in.) around the joint has been incorporated in the commentary to Part II of the 2002 AISC Seismic Specification. [ABSTRACT FROM AUTHOR]

Presents information on a study which used the results of bolted T-stub component tests and full-scale T-stub connection tests to develop and calibrate a comprehensive T-stub connection stiffness model. Mechanisms influencing the behavior of T-stub connections; Behavior of a connection incorporating T-stubs; Models of T-stub deformation component; Model limitations; Conclusions.

Presents information on a study which focused on the results of tests on T-stub specimens of bolted steel connections. Behavior of bolted connections; Tension bolt and flange strength; Conclusions.

Part II. Presents information on a research which determined the effect of structural phenomena on the behavior of the type of fully-restrained, steel moment-resisting frame connections that failed during the 1994 Northridge, California, earthquake. Experimental test setup and connection performance; Effect of composite floor slabs; Conclusions.

Recent experiments demonstrated that reduced beam section moment connections with some of the largest hot-rolled beam and column shapes (jumbo shapes) may not have sufficient ductility for high seismic applications if designed according to current design procedures. A parametric computational study was performed to evaluate potential changes to the design procedures to enhance the ductility of these connections with jumbo shapes. First, three-dimensional finite element models were developed and calibrated to match cyclic experimental results including load vs displacement response, panel zone deformations, and deformed shape. The models were then used to conduct parametric studies with inelastic monotonic loading to examine the effect of design parameters including beam flange reinforcing fillet weld size, panel zone strength and doubler plate location on fracture potential. The results showed that the size of the reinforcing fillet weld on the underside of the bottom flange has a significant impact on the local stresses and strains at the location of fracture initiation in the tests and that larger size fillet welds should be used with jumbo beams to mitigate the concentration of inelastic strains. The results also showed that joints with higher panel zone strengths lead to lower fracture potential and that moving the column web doubler plate outwards to the edge of the flange is another effective strategy to reduce local strain concentrations. The absence of local buckling in jumbo sections eliminates the strength degradation that limits demands on the welds and needs to be taken into consideration in their design. Recent experiments demonstrated that reduced beam section moment connections with some of the largest hot-rolled beam and column shapes (jumbo shapes) may not have sufficient ductility for high seismic applications if designed according to current design procedures. A parametric computational study was performed to evaluate potential changes to the design procedures to enhance the ductility of these connections with jumbo shapes (Fig. 1). First, three-dimensional finite element models were developed and calibrated to match cyclic experimental results including load vs displacement response, panel zone deformations, and deformed shape (Fig. 2). The models were then used to conduct parametric studies with inelastic monotonic loading to examine the effect of design parameters including beam flange reinforcing fillet weld size, panel zone strength and doubler plate location on fracture potential. The results showed that the size of the reinforcing fillet weld on the underside of the bottom flange has a significant impact on the local stresses and strains at the location of fracture initiation in the tests and that larger size fillet welds should be used with jumbo beams to mitigate the concentration of inelastic strains. The results also showed that joints with higher panel zone strengths lead to lower fracture potential and that moving the column web doubler plate outwards to the edge of the flange is another effective strategy to reduce local strain concentrations. The absence of local buckling in jumbo sections eliminates the strength degradation that limits demands on the welds and needs to be taken into consideration in their design. Unlabelled Image • Parametric analyses aimed at clarifying behavior of steel welded connections utilizing jumbo steel sections were conducted. • The reinforcing fillet weld should have a minimum 14 mm at the bottom beam flange CJP groove weld in jumbo sections. • The strength of panel zone in jumbo sections is suggested equal to 0.85 times the shear yielding strength in current codes. • The fracture potential was reduced when the doubler plates were shifted to the edges of the flanges. • A larger peak strength factor may be applicable for sections with b bf /2t bf < 6. [ABSTRACT FROM AUTHOR]

This article examines experimentally the behavior of transition steel connections between smaller rectangular and larger circular tubes in traditional-style Chinese buildings. The steel connections were subjected to combined constant axial load and lateral cyclic displacements. Tests were carried out on four 2/3 scale connections extracted from a prototype with two upper column lengths (or slenderness) and two levels of axial force. The influence of axial compression ratio and slenderness ratio on the mechanical behavior of the connections was assessed by looking at hysteretic performance, backbone curves, characteristic loads and corresponding displacements, ductility, energy dissipation capacity, and stiffness degradation. Test results showed that the primary failure modes were cracking of welds or base metal around the welds, and local buckling of the flange at the base of the rectangular steel tube column. The hysteresis loops were full and showed moderate degradation, indicating very good seismic performance for these steel connections. When failure occurred, the interstory displacement angle was between 2.2% and 2.8%, and the equivalent viscous damping coefficient was about 0.26–0.29. Based on the experimental research, an idealized bilinear backbone curve model was developed considering both stiffness degradation and second order effects. This simplified model provides both a yield and an ultimate strength and deformation capacity that can be used in design. [ABSTRACT FROM AUTHOR]

A shape memory alloy based articulated quadrilateral bracing system is developed and experimentally tested for seismic resisting applications. The articulated quadrilateral arrangement provides a scalable, reconfigurable, convenient means of combining nickel-titanium (NiTi) wires and energy dissipating elements. This configuration creates a system with an adjustable amount of recentering and damping, which could potentially be used in a wide variety of new and existing buildings. For these prototype tests, NiTi wire bundles were combined with long C-shaped dampers to create a system with a good balance of recentering and energy dissipation. The system was subjected to cyclic loading to assess the behavior. The system maintained strength, ductility, and recentering after being cycled to 2% drift, which is a typical maximum in structural systems if non-structural elements are to be preserved. An analytical case study demonstrated that shape memory alloy systems tend to distribute the deformation more evenly over the height of the structure compared to traditional systems, which is a desirable seismic performance characteristic. It is envisioned that, by using the same basic bracing setup, a wide range of force-deformation responses can be at an engineer's disposal. [ABSTRACT FROM AUTHOR]

Impact energy tests are an efficient method of verifying adequate toughness of steel prior to it being put into service. Based on a multitude of historical correlations between impact energy and fracture toughness, minimum impact energy requirements that correspond to desired levels of fracture toughness are prescribed by steel bridge design specifications. Research characterizing the fracture behavior of grade 485 and 690 (70 and 100) high-performance steel utilized impact, fracture toughness, and crack arrest testing to verify adequate performance for bridge applications. Fracture toughness results from both quasi-static and dynamic stress intensity rate tests were analyzed using the most recently adopted master curve methodology. Both impact and fracture toughness tests indicated performance significantly greater than the minimum required by material specifications. Even at the AASHTO Zone III service temperature, which is significantly colder than prescribed test temperatures, minimum average impact energy requirements were greatly exceeded. All master curve reference temperatures, both for quasi-static and dynamic loading rates, were found to be colder than the Zone III minimum service temperature. Three correlations between impact energy and fracture toughness were evaluated and found to estimate reference temperatures that are conservative by 12 to 50 °C (22 to 90 °F) on average for the grades and specimen types tested. The evaluation of two reference temperature shifts intended to account for the loading rate was also performed and the results are discussed. [ABSTRACT FROM AUTHOR]

• Formulation of an analysis method for infilled reinforced concrete (RC) frames, which is more accurate than equivalent-strut models and more computationally efficient than nonlinear finite element models. • Validation of the analysis method using experimental tests on infilled RC frames. • Demonstration of the capability of the proposed methodology to capture the damage patterns and global (load–displacement response of infilled frames). • The validation analyses are accompanied by a sensitivity study, demonstrating the impact of several model parameters on the obtained results. This paper presents a new modeling approach for masonry-infilled, reinforced concrete (RC) frames, based on the nonlinear truss analogy. The unreinforced masonry infill walls are modeled with truss cells containing horizontal, vertical and inclined elements. Zero-length macroelements are also used to account for the localized damage on mortar joints. The frame members are modeled with a recently proposed scheme that can account for inelastic response and can capture the effect of shear damage and failure of RC columns. The modeling approach is validated through analysis of experimentally tested masonry-infilled frames, and its capability in capturing the strength and damage patterns is evaluated. A sensitivity study is also provided, to elucidate the impact of several model parameters on the obtained analytical results. [ABSTRACT FROM AUTHOR]

Abstract: A half-scale interior beam-column connection incorporating superelastic nickel-titanium shape memory alloy (SMA) tendons was designed, fabricated, and tested to assess the feasibility of such a connection in a moment-resisting frame. This connection was compared to three other connections utilizing tendons made of steel, martensitic nickel–titanium, and superelastic nickel–titanium paralleled with aluminum. The connections with steel and martensitic nickel–titanium tendons rapidly lost their stiffness after being cycled beyond their elastic drift levels. The two tests with the superelastic nickel–titanium tendons showed significant recentering capabilities; they recovered a large portion of the post-elastic drift and showed promise for a material-based recentering moment connection. This novel connection was intended as a proof of concept that can be further developed in terms of practicality, ease of installation, and cost. [Copyright &y& Elsevier]

Abstract: A hybrid seismic device that provides both energy-absorbing and re-centering capabilities to overcome external forces is developed and evaluated. The hybrid device is composed of three main components: (1) a set of re-centering wires fabricated from shape memory alloy (SMA) material, (2) two energy-absorbing struts, and (3) two high-strength steel tubes to guide the movement of the hybrid device. The SMA wires are located within the guiding high-strength steel tubes and designed to be sufficiently long such that their deformation strain is within the 6% target strain limit. A conservative value of 6% strain, instead of 8%, or 10%, is adopted to (1) avoid the SMA stiffening phase that increases strength up to 5 times that of its forward transformation yield forces, resulting in a serious damage to the adjacent structural members, and (2) to retain the full re-centering capability of the SMA wires even when the hybrid device is under large displacement. The energy-absorbing struts are pin-connected outside of the guiding steel tubes and may be fabricated of mild steel or low strength aluminum. To reduce the possibility of buckling in the energy-absorbing struts when subjected to compression, they are designed to be stocky and seismically compact, or buckling restrained. An optimal proportion of the SMA wires and energy-absorbing struts is formulated such that the hybrid device retains re-centering capability, while maximizing energy dissipation. Results obtained through the seismic analysis reveal that the hybrid braced frame system exhibits a similar energy dissipation capacity to the buckling restrained braced system, while also having excellent re-centering capabilities. [Copyright &y& Elsevier]

To investigate the effectiveness of several seismic strengthening techniques, a full-scale unreinforced masonry (URM) structure was subjected to slowly applied lateral load reversals after the application of fiber reinforced plastic overlays, near surface mounted rods, and vertical posttensioning. Results showed that all techniques were effective for improving the seismic resistance of the previously tested URM building structure. Each system either increased the lateral in-plane strength and/or provided continuity of pier and spandrel elements over increased lateral displacements. In addition, the response of the test structure (overall height to base ratio of approximately one) showed that global issues such as flange effects, the effects of overturning moment, and global rocking can be substantial and must be considered. [ABSTRACT FROM AUTHOR]

A variety of elastic and inelastic analytical approaches were used to investigate the response of a full-scale unreinforced masonry (URM) structure tested in the laboratory. Elastic analyses, employing a three-dimensional finite element model, revealed little coupling between parallel walls, and pointed to the appropriateness of two-dimensional analytical tools for further simulation of the test structure. The nonlinear analytical methods employed included, in order of increasing complexity, a rigid body analysis, a two-dimensional nonlinear pushover analysis, and a three-dimensional nonlinear finite element analysis. All methods considered important structural characteristics such as failure modes of perforated walls, flange effects, and global overturning moment effect. All methods predicted the experimental behavior fairly well. Strengths and weaknesses of these analytical approaches are discussed, and recommendations for analyzing old URM buildings are presented. [ABSTRACT FROM AUTHOR]

A full-scale two-story unreinforced masonry (URM) building was tested in a quasistatic fashion to investigate the nonlinear properties of existing URM structures and to assess the efficiency of several common retrofit techniques. This paper presents the main experimental findings associated with the nonlinear properties of the original URM structure. The test structure exhibited large initial stiffness and its damage was characterized by large, discrete cracks that developed in masonry walls. Significant global behavior such as global rocking of an entire wall, and local responses such as rocking and sliding of each individual pier were observed in the masonry walls with different configurations. In addition, formation of flanges in perpendicular walls and overturning moments had significant effects on the behavior of the test structure. A comparison between the experimental observations and the predictions of FEMA 356 provisions shows that major improvements are needed for this latter methodology. [ABSTRACT FROM AUTHOR]

Based on the results of a full-scale lateral load test of a two-story unreinforced masonry (URM) structure, modifications are suggested for the model implied by FEMA 356 for the in-plane analysis of perforated URM walls. These modifications allow the model to address global issues such as flange participation, overturning effects, and global rocking. In addition, changes are proposed to the pier model as well as to the definition of effective pier height. Following a description of each modification, the analysis results obtained using the proposed model and FEMA 356 are compared with experimental results. In terms of base shear resistance, the proposed model displayed an average error (absolute value) of 13% compared with an average error of 21% from FEMA 356. In addition, the proposed model also provided more accurate representation of failure modes. The improved accuracy of the proposed model is primarily attributed to the consideration of global issues. The results of a parametric analysis are also presented to provide insight into the relative influence of each modification proposed. [ABSTRACT FROM AUTHOR]

The commentary to the AISC-LRFD Specification addresses the design of framing systems containing partially restrained (PR) connections, but it does not provide specific guidance on how to analyze these types of systems to determine appropriate internal forces for design. In addition, it provides little information on how to select an appropriate connection stiffnesses for design calculations, such as the calculation of effective length factors. This paper presents an approach that allows for the consideration of nonlinear connection response using commonly available elastic analysis software. In addition, the application of the direct analysis approach to PR framing systems is presented in the context of the proposed method for handling the connection nonlinearity. The direct analysis approach allows for stability to be assessed using the AISC-LRFD beam-column interaction equations with the axial strength term Pn determined based on the actual member length. This eliminates the complexity of determining effective length factors for partially restrained framing. [ABSTRACT FROM AUTHOR]

This study evaluates the feasibility of a new class of partially restrained connections using shape memory alloys. In the martensitic form, shape memory alloys (SMAs) have the ability to recover large residual deformations by heating the alloy above its transformation temperature. The proposed connection consists of four large diameter NiTi SMA bars connecting the beam flange to the column flange and serve as the primary moment transfer mechanism. Two full-scale connections were tested using the SAC loading protocol. The connections exhibited a high level of energy dissipation, large ductility capacity, and no strength degradation after being subjected to cycles up to 4% drift. Following the initial testing series, the tendons were heated to recover the residual beam tip displacement. After initiating the shape memory effect within the tendons, the connections were retested, displaying repeatable and stable hysteretic behavior. An additional test was performed under dynamic loading to examine the strain rate effects on the performance of the connection. The dynamic tests showed similar behavior, except for a decrease in energy dissipation capacity when compared to the quasi-static tests. [ABSTRACT FROM AUTHOR]

The Borax corporate headquarters building, a low-rise steel moment frame, was less than one year old when it sustained significant structural damage during the 1994 Northridge earthquake. Seventy-five percent of its steel moment-resisting connections suffered severe brittle fractures. This paper presents a detailed documentation of the forensic investigation performed on this structure immediately following the earthquake. A companion paper presents the findings from a subsequent computational investigation performed on the structure. The two primary failure modes at the Borax building were column flange fracture and pull-out of the girder flange from the column. The failures are primarily attributed to a fundamental flaw in the standard code-prescribed welded-flange bolted-web connection and the extreme ground motion at the site. The paper also describes the repairs made to the structure. These repairs were completed before the SAC research that now guides repair and retrofit of these structures was available. [ABSTRACT FROM AUTHOR]

In order to study the seismic performance of a Chinese traditional style steel-concrete composite frame, a half-scale prototype was designed for a region with intensity seven in the Chinese seismic design code. In the experiment, the El Centro, Taft, Lanzhou and Wenchuan ground motions with different peak accelerations (0.035 g, 0.1 g, 0.22 g, 0.4 g) were used to simulate earthquakes of different characteristics and intensities. The displacement response, restoring force and acceleration response of the measured structure were analyzed, and the hysteresis characteristics, failure mechanism, deformability and energy dissipation capacity of the model were quantified. The results show that the damage caused is concentrated in the beams and at the transition zone between the upper and lower column as evidenced by noticeable pinching of the hysteresis curves. The ultimate story drift reached is about 1/157–1/153 (0.65%), satisfying the elastic-plastic limits in the code. At a peak acceleration of 0.4 g, the stiffness of the specimen is 66% lower than that at a peak acceleration of 0.035 g. The most obvious structural response is under the excitation of El Centro wave, while the smallest is under the action of Wenchuan ground motion. The finite element software SAP2000 was used to analyze the failure of the specimen, the displacement time history curve and sequence of the plastic hinges. The calculated values of the finite element are in reasonable agreement with the experimental values, which can supply some reference to the practical engineering application. [ABSTRACT FROM AUTHOR]

The use of elastic analysis is prevalent in the design of building structures even under loading conditions where inelasticity would be expected. Accordingly, geometric and material properties used in the elastic analyses must be carefully selected to maintain accuracy. Steel-concrete composite columns experience different forms of inelasticity. Concrete cracking is the source of much of the inelasticity and occurs at relatively low levels of load, but partial yielding of the steel, slip between concrete and steel, and concrete crushing also contribute to losses in stiffness. In this paper, the behavior of composite columns is characterized at the cross section and member levels through comparisons between inelastic and elastic analyses. Then, through a broad parametric study, specific practical design recommendations are developed for the elastic flexural rigidity of composite columns for the determination of lateral drifts under service loads. The recommendations in this paper provide simple and robust values for the stiffness of composite columns to be used for drift computations involving lateral loads. [ABSTRACT FROM AUTHOR]

The direct analysis method is the primary means of assessing system stability within a standard specification. This method, and in particular its use of reduced stiffness, has been thoroughly validated for use in frames consisting of structural steel members. However, appropriate stiffness reductions have not yet been established nor has the method as a whole been validated for frames with steel-concrete composite columns. Through comparisons between second-order inelastic analysis results and results from the design methodology on a parametric suite of small frames, the current design provisions are evaluated in this paper. The results indicate that while the current design provisions are safe and accurate for the majority of common cases, there exist cases in which the current provisions result in high levels of unconservative error. Modifications to the current design provisions are proposed to address these issues. [ABSTRACT FROM AUTHOR]

Composite steel-concrete construction uses steel and concrete together to provide the possibility of a system with better performance, and/or lower cost, than using either material alone. This paper firstly subjectively evaluates the advantages and disadvantages of a number of composite concrete filled tubular (CFT) column-connection systems proposed/used around the world in terms of their likely acceptance in moment frames in New Zealand. Then, the cost of a conventional one-way moment-resisting steel frame system is compared with a similarly behaving frame using rectangular concrete filled steel tubular (CFT) columns. It is shown for these studies conducted on one-way frames that composite CFT column construction with beam end-plate connections is generally more expensive than conventional steel column construction. [ABSTRACT FROM AUTHOR]

Abstract: This paper deals with experimental investigations to study the seismic behavior of thick-walled circular hollow section (CHS) X-joints subjected to out-of-plane bending (OPB). Important geometric parameters were varied in designing three full-scale joint specimens in order to evaluate their effect on connection behavior. Test results indicated that the failure modes and the connection efficiency of these joints significantly depended on the brace-to-chord thickness ratio and the brace-to-chord diameter ratio . The tension fracture was identified as a critical failure mode for thick-walled X-joints with large . CHS X-joints with larger ratio were found to demonstrate better connection ductility and more satisfactory energy dissipating capacity than those joints with smaller ratio under cyclic OPB loading. This observation was further verified by the proposed simplified analytical model results. Finite element (FE) analyses were performed to simulate the experimental behavior and facilitate the interpretation of the important test observations. [Copyright &y& Elsevier]

Riveted steel connections were used throughout most of the United States for many years. The connections were commonly encased in massive but lightly reinforced concrete for fire protection. These older structures were designed with little or no consideration of seismic behavior, and today these buildings sometimes require seismic rehabilitation and retrofit, but little information regarding this behavior is available. The present paper provides information regarding the seismic performance of these older steel structures. An experimental study which evaluates the seismic behavior of subassemblages with T-stub and clip angle connections is described in detail. The results are analyzed. The strength, stiffness and ductility of the connections are shown to be related to the properties of the steel and the concrete, the mode of failure of the connection, and the concrete encasement. The hysteretic behavior, energy dissipation and deformation capacity of the connections are shown. Approximate models for predicting the strength, stiffness, and deformation limits are presented as practical implications of the research. [ABSTRACT FROM AUTHOR]

This paper presents the findings from a computational investigation performed on the Borax corporate headquarters building, a four-story steel frame structure in which 75% of the steel moment-resisting connections suffered brittle fractures during the 1994 Northridge earthquake. A companion paper provides detailed documentation of the forensic investigation and repair design performed immediately following the earthquake on this structure, which was less than one year old when the earthquake struck. This paper describes a series of preliminary analyses conducted shortly after the forensic investigation and repair were completed. The main objectives were to investigate the behavior of the structure during the earthquake, and to determine whether different levels of established, advanced analysis techniques could estimate the distribution and extent of the damage. The results showed that a three-dimensional nonlinear dynamic analysis using a site-specific accelerogram provides strong correlation with the observed damage, while elastic static and dynamic analyses, two-dimensional nonlinear static and dynamic analyses, and three-dimensional nonlinear static analyses show less correlation. In addition, the results indicate that substantial redistribution of forces may have occurred, and that force distribution most likely had a noticeable effect on the pattern of failures observed in the structure. [ABSTRACT FROM AUTHOR]