Guoqiang Li

Analysis of Circular Concrete-Filled Steel Tube Specimen under Lateral Impact

This paper mainly discusses the derivation and usage of simplified analysis model of circular concrete-filled steel tube specimen under lateral impact. At first, the robust software, LS-DYNA, is employed in this paper to simulate a test of circular concrete-filled steel tube (CFT) specimen under drop impact carried out by Li (2007). The numerical simulations results agree well with the experiment results and it shows good prediction of dynamic response of the CFT specimen under lateral impact could be achieved. Further analysis based on LS-DYNA model is then made to investigate the stain rate effect of the CFT column with fixed-simple supported ends. At last, a simplified analytic model is derived based on the combination of the tests results, the numerical simulation and theoretical analysis. The comparison between the maximum deflections at the mid-span obtained from the proposed simple analytical model and the numerical simulation shows that the proposed method gives good predictions of the maximum deflection of the CFT specimen under lateral impact.

Development of New-Type Buckling-Restrained Braces and Their Application in Aseismic Steel Frameworks

Two new-type BRBs, i.e. TJI-type and TJII-type, were developed at Tongji University. TJI-type was designed for small load-carrying applications while TJII-type for large ones. Full scale cyclic test results demonstrated stable hysteretic behavior and substantial energy dissipation capacity of the new-type BRBs. Hysteretic model and stiffness equation were established for the new-type BRBs, being capable of simulating accurately experimental behavior of the BRBs under low cyclic loading. BRB-moment frames (BRBF) and ordinary concentrically braced frames (CBF) were compared by means of elasto-plastic seismic analysis on a typical 8-story building, showing that under severe earthquakes BRB acted as structural “fuse”, to protect beams and columns from significant yielding, while ordinary braces buckled, and led to large amount of plastic hinges occurring in beams and columns and inter-story drift larger than 1/50. As an alternative application of BRBs, the structural system of simple-connected steel frame with buckling restrained braces was proposed for multistory buildings. By non-linear static and time-history analysis, the seismic behavior of this system was investigated. The results showed that this system had energy-dissipation behavior as good as steel moment frame. The superiority of this system in terms of seismic performance under extremely severe earthquakes was also verified by shaking table test on a two-story full-scale structure.

Large-Scale Testing of Steel Portal Frames Comprising Tapered Beams and Columns

Advanced analysis and design of steel frames can directly and exactly determine the ultimate system capacity without resort to simplified elastic methods of analysis and semi-empirical interaction equations (Chen, 1993). However, the application of advanced analysis methods has previously been based on steel frames comprising prismatic members. A research project has been conducted with the aim of developing concentrated plasticity methods suitable for practical advanced analysis and reliability-based design of steel portal frames with tapered members (Li, 2001). Two large-scale realistic tests were performed in order to provide experimental results for verification of the new analytical models, and to examine the important nonlinear effects that should be added in further theoretical research. Tested frames are identical in dimensions and with tapered beams and columns. One was subjected to incremental vertical loads and the other to simultaneous constant vertical loads and incremental horizontal loads. The details of the test program including the test frames, test rig and instrumentation, test procedure and results are given in this paper. Comparisons between design and analytical results are presented and discussed.

Blast test and numerical simulation of point-supported glazing

The blast resistance of point-supported laminated glass curtain wall has been investigated by means of field blast tests and numerical simulation. Nine site blast tests were carried out, considering two types of glass thickness and six TNT charges ranging from 0.4 to 30u2009kg. The overpressure and displacement time histories were measured and the failure modes were observed. The overpressure obtained from the measurement panel exhibited a typical pattern of near-field blast with a steep increase followed by a rapid decay within a few milliseconds. The displacement response of the laminated glass panels increased with the increase in the TNT charge almost linearly in the smaller tests (scaled distance ranging 4.5–7u2009m/kg1/3), which was in line with the increase in the blast impulse in these tests. The failure mode of the point-supported laminated glass panels was featured by tearing off of the polyvinyl butyral layer around the support area, while the glass shards still adhered to the polyvinyl butyral interlayer. Nonlinear dynamic finite element simulation agrees reasonably well with the results from the blast tests. Severe stress concentration has been predicted to occur at the rim of the support holes, leading to initiation of failure at these supports, and this also agrees with the failure mode observed from the blast test. Finally, parametric studies are carried out to investigate the influence of TNT charge weight and the geometric parameters of the panel on the blast response of the glass curtain wall.

Study of the Anchorage Connections for Buckling Restrained Braces Part 1: Experimental Investigation:

This is the first of the two companion papers dealing with anchorage connection for buckling restrained braces (BRBs) used in reinforced concrete frames. In this paper, configuration details of an anchorage connection are proposed. Eight comparative specimens are designed to investigate the monotonic and cyclic behaviors of the proposed connection under tension/compression, shear and combined tension/compression and shear conditions. Test results indicate that static and hysteretic behaviors of the connection under tension/compression are much better than those under shear. In order to guarantee the energy dissipation of BRBs, the connection should work in elastic state to prevent low cycle fatigue failure and to reduce the deformation of the anchorage connections. Furthermore, the design method of the anchorage connections presented in the related Chinese codes (GB 50010–2010 and GB 50011–2010) is examined against the test results. It is found that the code method is accurate enough for predicting the load-bearing capacity of the connections under mere tension and mere shear condition, but is too conservative for prediction under combined tension and shear. At last, the design suggestion is proposed for the anchorage connection against the test results. Due to limitation of the test results, theoretical study is carried out in Part 2 of the companion papers.

Study of the Anchorage Connections for Buckling Restrained Braces Part 2: Theoretical Study

This paper investigates behaviors of the anchorage connections for buckling restrained braces (BRBs). Finite element (FE) models are established by using software ABAQUS to simulate some tests reported in Part 1 of the companion papers. The material nonlinearities of concrete, anchor bars and anchor plates with the contact property between them are considered in the FE models. A numerical formula is developed for predicting the shear stiffness of anchor bars based on the results from the parametric study using ABAQUS. A formula dealing with the tensile stiffness of the anchor bars is presented relied on the theoretical study. Both of the proposed formulas are verified with the test results. Some design suggestions of the anchorage connections for buckling restrained braces are presented on the basis of the theoretical and experimental studies.

Spline Finite Element Methods for Analysis of Axially Restrained Steel Beams Subjected to Elevated Temperatures in Fire

A spline finite beam element for analysis of axially restrained steel beams subjected to elevated temperatures in fire is presented. Both geometric nonlinearity and material nonlinearity are integrated in the proposed method. Governing equations of the beam are established according to the internal-force and external-force equilibriums at each node of the elements representing the beam, and the nonlinear equations system is solved by the Newton-Continuation method. This strategy can avoid the building of the elemental and globe stiffness matrix, which may be complex when involves the second-order effect of axial force and elastic-plasticity of steel at elevated temperatures. Numerical examples of using the method proposed are presented. The influence of non-uniform temperature distributions is discussed. The structural responses, which include the deflection, axial force and moment at middle-span of the example beam, are calculated using both the presented spline finite element method (SFEM) and general finite element method (FEM) with shell elements. Comparisons of the results show that the spline finite beam element method is computationally economical and precise.