Sumei Zhang

Behavior of Steel Tube and Confined High Strength Concrete for Concrete-Filled RHS Tubes:

This paper presents an experimental study of the separated behavior of short (L/H=3) high strength concrete-filled rectangular hollow section (RHS) tubes concentrically loaded in compression to failure. A total of 50 specimens were tested. Experimental results showed that the concrete strength influenced the failure pattern of the specimen. The height-to-breadth ratio of the rectangular tube (varying from 1.0 to 1.6) had no evident influence on the ultimate bearing capacity of the specimen. Then based on the experimental results, a numerical separation method was successfully used to separate the compressive load carried by the steel tube and the core concrete. The equivalent One-Dimensional nonlinear stress-strain models of the steel and the confined concrete were suggested, which can be used to determine the overall behavior of the high strength concrete-filled RHS tubes. The stress-strain models have been used to numerically analyze the behavior of high strength concrete-filled RHS tubes. The numerical results are compared with the experimental results and they agreed well with each other.

Behaviour of High Strength Concrete-Filled Slender RHS Steel Tubes

An experimental study of the behaviour of high strength concrete-filled slender rectangular hollow section (RHS) tubes under the combined actions of axial compression and bending moment is presented. A total of 26 specimens were tested. The main parameters considered in the test were slenderness ratio, depth-to-breadth ratio, steel-to-concrete area ratio and eccentricity-to-depth ratio. The experimental results showed that the ultimate capacity of test specimens decreased rapidly with increase of slenderness ratio and eccentricity-to-depth ratio. For the specimens with depth-to-thickness ratio larger than 50, local buckling failure occurred prior to the ultimate capacity. A nonlinear analysis program, BC, was developed to analyze the behaviour of high strength concrete-filled RHS tubes. A comparison for ultimate capacity showed that the theoretical results agreed very well with the experimental results. The depth-to-breadth ratio (varying from 1.0 to 1.6) showed little influence on the stability capacity of the specimens. The comparison of the experimental results with the results calculated by the design equations in the codes, such as LRFD, EC4 and AIJ showed that EC4 closely predicts the ultimate capacity of the specimens.

Hysteretic analysis of steel plate shear walls (SPSWs) and a modified strip model for SPSWs

Steel plate shear walls (SPSWs) have become more and more popular in recent years because of their potential huge energy dissipation capacity and ductility under lateral loads. Due to their low cost and fast construction, SPSWs have potential application in practice. The finite element software ANSYS applied to the analysis of the hysteretic behavior of SPSWs is described in this paper first. It was found that compressive stress existed in SPSWs and the effects became more evident with decreasing height-to-thickness ratio. This was validated by comparing theoretical and experimental test results. Secondly, based on the analytical results, a modified strip model is proposed. In the modified model, the compressive effects in the panel were taken into account and it was then found that the load-carrying capacity and the energy dissipation capacity agreed well with the already carefully validated experimental results.

Behaviour of Filled Rectangular Steel HSS Composite Columns under Bi-Axial Bending:

The purpose of this study was to investigate the behaviour of concrete-filled rectangular steel hollow structural section (HSS) columns formed by slender plates with large depth-to-width ratio subjected to bi-axial bending. As part of this study, four large concrete-filled thin-walled rib-stiffened rectangular HSS columns have been tested. Their steel tubes possess a depth-to-width ratio of 2.38 and a depth-to-thickness ratio of 175. Rib stiffeners were welded to the plate walls such that the stiffened plate width-to-thickness ratio (= 45) was less than that specified (= 60) in the Chinese design code. The results showed that local buckling of steel plate appeared after the specimen reached the ultimate capacity. Also, the fiber element analysis method is adapted to analyze the behaviour of specimen, in which the change of neutral axis position is considered. At last, the experimental results are compared with the values calculated from design codes, namely EC4, LRFD, CECS and DBJ. The results show that all codes provide safe ultimate capacities. Among them, the capacities calculated from DBJ yield results closest to the experimental ones and the other three design codes produce safety over 20%.

Performance Testing and Cyclic Behavior of Buckling-Restrained Braces with H Cross Section Unrestrained Segments

The hysteretic behavior of four buckling-restrained braces (BRBs) with H cross section unrestrained segment was tested under cyclic load. The transformation of the unrestrained segments section from crisscross shape to H shape can improve the moment-resistance capacity of unrestrained segment significantly and avoid buckling instability of unrestrained segment effectively due to evident stiffness enhancement. BRBs were designed according to Chinese codes, the load-carrying elements of BRBs were fabricated with Chinese Q235 steel. In the process of experiment, BRBs did not buckle, BRBs could undergo fully-reversed axial yielding cycles without loss of stiffness and strength, the ductility and energy absorption capacity of BRBs are large enough to withstand major earthquake. The resilience model can be simplified to a symmetrical bilinear resilience model. The ratio of width to thickness of inner core has a little influence on the mechanical behavior and energy-dissipation capacity of BRBs. A suggestion for design improvement of BRBs was proposed according to the failure modes of BRBs.

Behavior and Strength of Circular Tubed Steel- Reinforced-Concrete Short Columns under Eccentric Loading

This paper presents the results of experimental studies on circular tubed steel-reinforced-concrete (TSRC) short columns subjected to axial and eccentric loading. A total of 12 columns with the key parameters of eccentricity ratio and diameter-to-thickness ratio of the steel tube were tested. The effect of shear studs on the co-work behavior of concrete and shaped steel was studied. The test results indicated that the shear studs affected little on the failure mode, bearing capacity and ductility of the eccentrically loaded circular TSRC short columns. Elastic-plastic analysis for the steel tube showed that the tubes at the compression side began to yield when the load approximately reached 90% of the peak load. Fiber-based numerical models for circular TSRC short columns were established and the results accorded well with the experimental results. Furthermore, the whole section plastic assumption in EC4 was adopted to determine the section capacity interaction diagram for circular TSRC columns.

In-Plane Stability of Fixed Concrete-Filled Steel Tubular Parabolic Arches under Combined Bending and Compression

AbstractThe current codes and specifications use the equivalent beam-column method to predict the in-plane stability capacity of concrete-filled steel tubular (CFST) arches. Using this method, the effects of the rise-span ratio and the nonuniform moment on the stability capacity of CFST parabolic arches are not considered. This may induce a difference between calculation results and actual structural stability capacity. To study the effects of the rise-span ratio and the nonuniform moment, six fixed CFST parabolic arches, with rise-span ratios of 1/4.5, 1/6, and 1/9, were tested and analyzed in this study. The failure patterns and mechanisms were studied. The confining effect of the steel tube to the concrete at failure was investigated. The influence of the rise-span ratio and loading conditions on the in-plane stability of fixed CFST arches was also considered. A nonlinear elastic-plastic finite-element (FE) model was used to predict the buckling behavior of the fixed CFST parabolic arches. Based on the...

Dynamic analysis of concrete-filled steel tube composite frame against progressive collapse based on benchmark model:

To provide a unified assessment standard in both seismic analysis and progressive collapse analysis, a benchmark model with joint substructure for concrete-filled steel tube composite frame is developed and studied by alternative path method. The effects of failure period on dynamic response of the model and two types of dynamic increased factor are analyzed. Demand–capacity ratio is used to evaluate the progressive collapse behavior of the model. The results show that beyond 0.5 time of natural vibration period, the failure period has almost no effect on the dynamic response of the model. The peak moment–nominal moment capacity ratio of the beams connected to the removed column indicates that the closer the column gets to side column with pin connections, the more potential it has to trigger collapse. The bending stiffness of beam has little effect on the dynamic response of the model when it is greater than the doubled value. Displacement-based dynamic increased factor in linear static analysis is almost identical to load-based dynamic increased factor in linear static analysis in each case of column removal. Compared with the value of load-based dynamic increased factor, the value of displacement-based dynamic increased factor in nonlinear analysis is closer to the recommended value of 2.0 in GSA.

Partial interaction analysis of multi-layered composite beams accounting for time effects

Innovative structural solutions have been achieved in the fields of structural and mechanical engineering by combining different materials to produce more economical and efficient elements. The interaction between different materials has been achieved in various manners and this paper is concerned with those situations in which layers of different materials are interconnected by means of flexible mechanical devices. Of particular interest to this paper are composite members with partial shear interaction which have been studied for several decades. One of the first papers dealing with the partial interaction analysis of two-layered composites was the one by Newmark et al. [1] who focussed their attention on steel-concrete composite beams. Due to the wide acceptance of this work, its formulation is simply referred to in the literature as Newmark model. This paper extends the applicability of this model to study the time-dependent behaviour of multi-layered composite beams with partial shear interaction formed by n layers. A generic displacement-based finite element formulation is presented for the derivation of n-layered beams and is then applied to the case of a three-layered element representing the particular case of a composite steel-concrete beam stiffened by a longitudinal steel plate in which the partial interaction occurs between the slab and the steel joist as well as between the joist and the stiffening plate. The accuracy of the proposed procedure is validated against closed form solutions for the two limiting cases in which both shear connection stiffnesses tend to infinity, representing the full interaction condition; and also where only one connection stiffness is infinitely high, thus degenerating to the conventional two-layered composite partial interaction behaviour. Applications are then presented to investigate the effects of the two interface connection stiffnesses on the structural response of the stiffened composite beam. For this purpose, different lengths are considered for the longitudinal plate and the time-dependent behaviour of the concrete is modelled by means of the step-by-step method.

Behaviours and Strengths of Concentrically Loaded Short Concrete-filled Steel HS Columns with Different Cross-section Geometries

This paper presents the stress distribution, confinement distribution and complete average longitudinal stress-strain curves for concentrically loaded short concrete-filled steel circular, octagonal, square and rectangular hollow section (HS) columns using 3-D finite element (FE) analyses. The curves predicted by FE analyses are in good agreement with those obtained from previous experimental work. The compressive design strengths and the compressive moduli of concrete-filled steel HS columns are also obtained. A unified method is proposed for the design of concentrically loaded short concrete-filled steel HS columns with different cross-section geometries.