Composite Moment-resisting Frame Research Articles

Experimental study on a new V-cut RBS and CFT connections with bidirectional bolts under cyclic loadings

This paper presents experimental investigation on evaluation of performance of a new type of steel reduced beam section (RBS), designated as V-cut, and on its role in improving overall safety of RBS-CFT connections subjected to cyclic load. Detailed design steps adopted for design of the V-cut RBS with lower depth of cut, as compared to that in the conventional radius cut RBS, are reported in this paper. Behavior of two types of steel RBS and concrete filled tube (CFT) connections with bidirectional bolts were examined. An experimental study was performed to compare the performance of V-cut RBS with that of the conventional radius cut RBS under cyclic loading. It exhibited improved hysteretic behavior, and the new RBS-CFT connection is found to be semi-rigid in nature. Test results show that the energy dissipation in the composite steel connections with V-cut RBS is higher than that with radius cut RBS. The application of V-cut steel flange beam effectively enhanced ductility and reduced the residual torsional deformation. It reached a rotational capacity of 0.04 radians without any damage in the joint panel region, and thereby meets the seismic provisions of the AISC as a special composite moment-resisting frame. Further, a simplified numerical simulation of force-deformation hysteretic behavior of RBS-CFT connections was carried out using OpenSees software. Simulated force-deformation hysteresis loops are found to be in close agreement with those obtained from experimental investigation.

Assessment of Seismic Behavior Factor of Code-Designed Steel–Concrete Composite Buildings

In this study, the seismic behavior factor of steel–concrete composite buildings was examined. For this purpose, 5-, 10-, 15- and 20-story composite moment-resisting frame (CMRF) buildings having concrete-filled steel tube columns and composite beams were designed at medium ductility (DCM) and high ductility (DCH) levels as per the regulations of Eurocode 8. Examined DCM structures were designed for a PGA of 0.2 g while DCH structures were designed for a PGA of 0.4 g. SeismoStruct software was utilized in the design and performance assessment of the case study structures. Nonlinear static pushover and incremental dynamic analyses were used. In the pushover analysis, the uniform and triangular load distributions were adopted while 12 earthquake ground motions were employed in the dynamic analysis. The effect of ductility levels and number of stories on the seismic behavior of CMRFs was studied using the results of the nonlinear analysis. To this, the variation in the lateral response, global yielding value, code-based behavior factor and component, and dynamic behavior factor were presented for CMRF structures with DCM and DCH. It was observed that the behavior factor of all CMRFs exhibited well above the design assumptions, especially DCM class CMRFs.

Hysteresis performance of through bolted connections in CFST frame

This paper presents an experimental study on the seismic performance of composite structural frame systems consisting of concrete-filled steel tubes (CFSTs) and steel beams. The modified, extended end-plate connections were fabricated by straight through bolt for square columns and split bolt for the circular column with a curved endplate. Half-scale CFST composite moment resisting frames were tested under displacement-controlled quasi-static lateral cyclic load. Circular CFST columns possess better confinement than square CFST columns, but the application in construction is restricted due to the difficulty in joining with the steel beams. The present study investigates the strength, stiffness degradation, ductility, failure mode, and energy dissipation characteristics corresponding to the inter-story drift. The results from the tests indicate that the seismic resistance is at par with the American Institute of Steel Construction (AISC) seismic recommendations for composite special moment-resisting frame, and hence the split-bolt assembly can be used as an effective alternate for connection in circular columns. This work also tries to impart the experimental database on the effect of increasing the number of the bay in the resisting direction. Single-bay and double-bay frames were compared to quantify the improvement in seismic performance.

Seismic performance evaluation of regular and irregular composite moment resisting frames

Abstract In this study, the seismic behavior of regular and irregular composite moment resisting frame (CMRF) buildings was investigated. To this aim, 5, 8, 10, 13 and 15-story CMRFs having concrete filled steel tube columns and composite beams were designed at high ductility level and their performances were evaluated comparatively. The case study CMRF structures were categorized into two groups as regular and irregular in elevation. Examined irregular structures have setbacks in different story levels. During the design and performance analysis, SeismoStruct software was employed. Nonlinear static pushover and incremental dynamic analyses were used in the seismic performance assessment. The uniform and triangular load distributions were considered in the pushover analysis while a total of 22 earthquake acceleration records were utilized in the dynamic analysis. The variation in the lateral response, global yielding value, interstory drift, behavior factor, inherent strength factor, overstrength factor, and ductility factor were examined for the regular and irregular CMRF structures. It was observed that the regular CMRFs were more consistent with the design assumptions as compared to the irregular ones. Moreover, the former exhibited more uniform non-elastic demands over the building height according to the results of the incremental dynamic analysis. Under the seismic scenario adopted, all the building types yielded higher values of the behavior factor complied with the limits available in the code.

Finite Element Analysis of Weak-Axis Composite Connections Under Cyclic Loading

This paper describes a numerical study on weak-axis composite connection through the nonlinear finite element program ABAQUS. After the simulation and validation of experimental results, a total of 16 models were created to investigate the influence of the different parameters on the structural performance, and their hysteresis responses, rupture index distribution of beam flange welds were discussed in detail. The RBS connection scheme could develop extensive inelastic deformation in RBS region, thus reducing the weld rupture possibility. The thicker the concrete slab, the larger the bending moment under positive bending, and the higher the RI values at the beam bottom flange weld and also the neutral axis. The structural behavior was insensitive to the variation of the parameter reinforcement ratio as the reinforcements did not work well, and it is recommended to arrange reinforcements according to the construction requirements. Changing the weld access hole form has a little influence on the bearing capacity and rotation capacity, but the PEEQ and RI distributions are sensitive to this parameter. The design option of long access holes could provide a further means to reduce the fracture possibility of beam flange groove weld to a reasonable level, thus achieving a favorable performance of weak-axis column bending connections in a composite moment-resisting frame.

Seismic performance of composite moment-resisting frames achieved with sustainable CFST members

The main objective of the research presented in this paper is to study the bending behaviour of Concrete Filled Steel Tube (CFST) columns made with Rubberized Concrete (RuC), and to assess the seismic performance of moment-resisting frames with these structural members. The paper describes an experimental campaign where a total of 36 specimens were tested, resorting to a novel testing setup, aimed at reducing both the preparation time and cost of the test specimens. Different geometrical and material parameters were considered, namely cross-section type, cross-section slenderness, aggregate replacement ratio, axial load level and lateral loading type. The members were tested under both monotonic and cyclic lateral loading, with different levels of applied axial loading. The test results show that the bending behaviour of CFST elements is highly dependent on the steel tube properties and that the type of infill does not have a significant influence on the flexural behaviour of the member. It is also found that Eurocode 4 is conservative in predicting the flexural capacity of the tested specimens. Additionally, it was found that the seismic design of composite momentresisting frames with CFST columns, according to Eurocode 8, not only leads to lighter design solutions but also to enhanced seismic performance in comparison to steel frames.

The experimental behavior and simple modeling of joints in composite MRFs

In the case of composite steel-concrete construction, the seismic performance of Moment Resisting Frames (MRFs) is not well-known as for reinforced concrete or steel construction because the coupling of the two materials results in different mechanisms with asymmetric behaviors in the case of reversed loads.The performance of the frames under seismic actions is dependent on all components, beams, columns and joints. However, the modern approach of the international codes (Eurocode) consists of a hierarchy of resistances governing the failure mode, i.e., the ductility of the structure.To contribute to a better understanding and assessment of the actual behavior of steel-concrete composite joints, this paper discusses the experimental results of two full-scale steel-concrete composite joints (a welded and a bolted joint) tested under cyclic loading.The two full-scale composite exterior joints were designed to localize the damage at the composite beam end with respect to the designed capacity of the MRFs. Therefore, the joints contribute to the deformability of the system in the elastic field. The specimens were highly instrumented; the experimental results are presented in terms of global and local measures. For the global response, the main role of the composite beam is highlighted. The performance of the joints is described in terms of resistance, ductility, dissipated energy and stiffness degradation. The contribution of the composite beam to the global ductility is evaluated in terms of rotational capacity, and an “equivalent” plastic hinge length is evaluated. A simple model for the estimation of the nonlinear behavior of the joints, which is suitable for analyzing the global behavior of framed composite structures, is proposed.

Moment resistance statistical distribution of beam-to-column composite joints

In seismic design of steel–concrete composite moment resisting frames, the randomness of beam-to-column joint rotational response can affect the location of dissipative zones. In fact, in case of full-strength joints, the dissipation of the earthquake input energy occurs at the beam ends; conversely, in case of partial-strength joints, the connection components of beam-to-column joints are involved. Within this framework, random material variability of joint components plays an important role, because it affects the joint flexural strength and, as a consequence, also the plastic rotation supply. Therefore, within the framework of a research program aimed at the evaluation of the seismic reliability of steel–concrete composite frames including random material variability, this paper focuses the attention on the analysis of the influence of random material variability on the rotational response of beam-to-column joints. In particular, the aim of the work is the evaluation, by means of Monte Carlo simulations, of the statistical distribution laws of the parameters describing, from the overall point of view, the rotational behaviour of beam-to-column joints. Such distribution laws represent important input data for a complete probabilistic seismic demand analysis of steel–concrete composite moment-resisting frames where the joint modelling is performed by using rotational spring elements whose parameters are selected as random values satisfying the distribution laws previously derived.

Seismic performance of a 3D full‐scale high‐ductility steel–concrete composite moment‐resisting structure—Part I: Design and testing procedure

AbstractA multi‐level pseudo‐dynamic (PSD) seismic test programme was performed on a full‐scale three‐bay two‐storey steel–concrete composite moment‐resisting frame built with partially encased composite columns and partial‐strength connections. The system was designed to provide strength and ductility for earthquake resistance with energy dissipation located in ductile components of beam‐to‐column joints including flexural yielding of beam end‐plates and shear yielding of the column web panel zone. In addition, the response of the frame depending on the column base yielding was analysed. Firstly, the design of the test structure is presented in the paper, with particular emphasis on the ductile detailing of beam‐to‐column joints. Details of the construction of the test structure and the test set‐up are also given. The paper then provides a description of the non‐linear static and dynamic analytical studies that were carried out to preliminary assess the seismic performance of the test structure and establish a comprehensive multi‐level PSD seismic test programme. The resulting test protocol included the application of a spectrum‐compatible earthquake ground motion scaled to four different peak ground acceleration levels to reproduce an elastic response as well as serviceability, ultimate, and collapse limit state conditions, respectively. Severe damage to the building was finally induced by a cyclic test with stepwise increasing displacement amplitudes. Copyright © 2008 John Wiley & Sons, Ltd.

Seismic Performance Evaluation of a Large-Scale Composite MRF Using Pseudodynamic Testing

The seismic performance of a composite moment resisting frame (MRF) comprised of concrete filled tube (CFT) columns and wide flange beams was investigated experimentally. The four-story composite MRF test structure was designed using performance-based design concepts. The performance objectives include achieving: (1) the operational performance level under the frequent occurrence earthquake; (2) the life safety performance level under the design basis earthquake; and (3) the collapse prevention performance level under the maximum considered earthquake. The hybrid pseudodynamic test method was used to subject the test structure to these various seismic input levels. P-Δ effects associated with the gravity frames in the prototype building were included analytically in the tests. Results from the tests indicated that the structural performance under the simulated seismic loading was consistent with the expected performance for all three earthquake levels, indicating that effective seismic performance of comp...

Modelling of the panel zone in steel and composite moment frames

This paper deals with the modelling of the panel zone region within beam-to-column connections in steel and composite moment-resisting frames. Existing analytical models for representing the panel zone response are first reviewed and their scope and limitations are discussed. A new approach, which is particularly suited for modelling steel and composite joints within frame analysis procedures, is then proposed and described. The method rationally accounts for the effect of different boundary conditions, as well as shear and flexural deformation modes, in evaluating the elastic and inelastic response. Validation of the proposed approach is carried out through comparisons against available experimental results in addition to more detailed continuum finite element analyses. The results demonstrate that the approach developed provides a more realistic representation of the behaviour in comparison with available models, especially in the case of composite connections. It is shown that, for composite joints, commonly used simple moment–distortion relationships may not be adequate. This is primarily due to the dependency of the behaviour on the internal force distribution at the joint. The study describes the implementation of the suggested approach within frame analysis procedures, and substantiates the important role played by the panel zone in the response of moment frames under lateral loading conditions.

Non-linear analysis of steel–concrete composite frames with full and partial shear connection subjected to seismic loads

The seismic performance of moment-resisting frames consisting of steel–concrete composite beams with full and partial shear connection is investigated. To this end, six full scale composite substructures with headed stud shear connectors have been tested and the corresponding inelastic response to both monotonic and variable reversed displacements have been investigated. Three-dimensional finite element models of the substructures set with the ABAQUS code and based on shell elements are established in order to evaluate different modelling assumptions and local effects; and to calibrate a one-dimensional model conceived with the Drain-3DX code relying on layered beam–column elements. The one-dimensional model is then exploited for a parametric study on two four-storey frames by means of non-linear dynamic analyses. The analyses have revealed that composite frames with a low shear connection degree of about 0.4 perform as well as their companion frames with full shear connection under severe seismic loads. Nonetheless, the shear connection degree should be high enough in order to protect shear connectors in the central part of beams from failure. Although their equivalent damping is not very high, shear connectors could reduce the ductility demand on other parts of a composite frame, such as beam ends or partial strength beam-to-column joints. This design option could provide a further means to achieve a favourable performance of a composite moment-resisting frame, in addition to the benefit of cost reduction.