Lei Zhang

Zhejiang University | ZJU · Department of Civil Engineering

Steel-concrete composite walls, valued for their capacity to combine the strengths of steel and concrete, have become a prevalent construction choice. During the past few decades, the performance of steel-concrete composite walls has been studied by means of structural tests, theoretical analysis, and numerical simulation. Different types of steel-...

Compared to traditional robotic systems, small-scale robots, ranging from several millimetres to micrometres in size, are capable of reaching narrower and vulnerable regions with minimal damage. However, conventional small-scale robots' limited maneuverability and controlability hinder their ability to effectively navigate in the intricate environm...

The animation visualizes the capsule robot's propelling motion driven by an excitation force. This simulation was conducted using the commercial finite element package ABAQUS by Mr Yujia Zhang.

Compared to traditional robotic systems, small-scale robots, ranging from several millimetres to micrometres in size, are capable of reaching narrower and vulnerable regions with minimal damage. However, conventional small-scale robots’ limited maneuverability and controlability hinder their ability to effectively navigate in the intricate environm...

The local buckling of I-section beams is investigated with the flange–web interactions taken into account. Using numerical results employing the finite element method and a semi-analytical method, the flange–web interactions of I-sections and their effects on the buckling stresses are explored and discussed. Simple approximate solutions for the buc...

The local buckling of I-section columns is investigated in this paper, where the interaction between the web and flanges is taken into account. An analytical method is first developed based on the classical theory of the elastic buckling of thin plates, with which the main parameters affecting the interaction between the web and flanges are analyze...

The buckling behaviour and design of aluminium alloy single-angle members connected by one leg are investigated in this study. Buckling tests were carried out on eight simply supported aluminium alloy single-angle members with the load applied on one leg only. Finite element models were established and validated against test results in this study a...

Multi-cellular concrete-filled steel tubular (CFST) columns have been widely used in frame structures for seismic resisting purposes. In this paper, the seismic performance of single-story composite frame structures, consisting of T-shaped multi-cellular CFST (TM-CFST) columns connected with steel beams, was investigated. Four specimens of the comp...

Multi-cellular L-shaped concrete-filled steel tubular (MCL-CFST) column is an improved L-shaped CFST column, which is composed of multiple rectangular steel tubes welded by U-shaped steel plates and then filled with concrete. The global stability capacity of MCL-CFST slender columns is vital for engineering applications. However, few investigations...

The behaviour and design method of 7A04-T6 high-strength extruded aluminium alloy lipped angle columns in axial compression are investigated. First, compressive tests on 27 pin-ended lipped angle columns of various dimensions were conducted. Measurement on initial geometric imperfections and tensile coupon tests were also performed. Second, the fin...

The concrete-filled wide rectangular steel tube (CFWRST) columns, with the aspect ratio of cross-section greater than 2.0, have attracted much attention in practice. Existing studies on the concrete-filled rectangular steel tube (CFRST) members have shown that the aspect ratio of cross-section is a main parameter controlling their behaviors under v...

With the development of pre-fabricated composite structures, concrete filled steel tubular (CFST) columns have been widely used, and researches on T-shaped CFST slender columns have attracted much attention. Since ordinary T-shaped CFST columns have weak constraint on concrete at the sectional concave angle region and local buckling easily occurs i...

Multi-celled concrete filled steel tubular walls (MCFSTWs) have been widely used in engineering practice. A high MCFSTW can be constructed by assembling two medium-height wall segments that are butt welded with the connector. At the connecting part between two wall segments, the connector, welding seams and steel plates of upper and lower wall segm...

Multi-celled corrugated-plate concrete-filled steel tubular (MC-CFST) member is an innovative type of composite member in engineering structures, which consists of steel corrugated plates with infilled concrete and concrete-filled steel tubes (CFSTs). In this paper, the flexural behavior of MC-CFST members was investigated through experimental, num...

Concrete-filled steel tubular (CFST) column has been widely used in engineering practice. In the process of assembling two columns to form a slender member, assembling errors (AE) are inevitably produced at the section of connection. When the AE are too large, the global buckling resistance of slender column would be significantly affected. Therefo...

The outstand flanges of aluminium alloy angles are sensitive to local buckling due to the low elastic modulus of material. To improve the sectional buckling stress, lips could be introduced to improve the stability behaviour of the outstand flanges. This paper presents an equilibrium approach and a simplified energy method for the local and distort...

The concrete-filled wide rectangular steel tubular (CFWRST) column is attracting more and more attention in engineering practice. The aspect ratio of CFWRST section is normally 2.0–3.0, which exceeds the limitation in existing studies, being less than 2.0. The finite element (FE) analysis has been widely used in investigating behavior of the concre...

In recent years, the concrete-filled steel tubular (CFST) columns with large cross-sectional aspect ratios have been paid much attention for practical engineering applications. By installing bolts to connect opposite surfaces of the steel tubes in bolt-connected CFST columns, the axial resistant behavior of CFSTs with large cross-sectional aspect r...

In recent years, the concrete-filled narrow rectangular steel tube (CFNRST) has drawn much attention for practical engineering applications. Compared with the commonly used concrete-filled rectangular steel tube (CFRST), the cross-sectional aspect ratio (the ratio between widths of wider and narrower sides of the steel tube) of CFNRST is larger and...

Profiled steel sheets are widely used in composite wall systems to form profiled double-skin composite walls (PDSCWs), serving as structural components in low-and medium-rise building structures. By using the profiled faceplates with re-entrant corrugations, the trough regions not only form vertical ribs to enhance the stability performance of the...

Elastic buckling of stiffened steel plate walls (S-SPWs) under combined compression and shear was studied focusing on the stiffness demand on stiffeners to implement subpanel’s buckling mode. Flat-bars and closed form stiffeners were considered. Threshold stiffness of stiffeners is presented for elastic buckling of subpanels of S-SPWs in pure compr...

The concrete filled narrow rectangular steel tube (CFNRST) member is being increasingly used in the apartment buildings in China. Experimental study is conducted on the behavior of CFNRST members subjected to combined compression and uniaxial bending about the weak axis. Eleven specimens were fabricated considering the variation of key parameters i...

Seismic force reduction factor (SFRF) spectra of shear-type multi-degree-of-freedom (MDOF) structures are investigated. The modified Clough model, capable of considering the strength-degradation/hardening and stiffness-degradation, is adopted. The SFRF mean spectra using 102 earthquake records on a typical site soil type (type C) are constructed wi...

A new theory for the buckling and nonlinear analysis of circular arches with shear deformation is developed, the theory is based on the variational principle in which the nonlinear strain energy of all stress components are included. For arches subjected to a uniform constant-directed radial load, internal forces and deformations including shear de...

Purlins are usually connected to roof sheeting by sliding-clips, while wall sheeting is often screw-fastened to girts. This paper investigates the buckling of such two types of parallel purlin/girt systems inter-connected by multiple lines of sag rods. One single purlin braced by one sag rod at any place along the span is first analyzed, and its bu...

The compressive stress is remarkable in design of steel plate walls (SPWs) for high-rise buildings. Stiffeners are required to avoid the compressive buckling in service limit state. This paper first studies the elastic stability of horizontally stiffened steel plate walls (S-SPWs) in compression. The effect of stiffener torsional stiffness on elast...

A unified model that can be used to study both distortional buckling and global lateral buckling of cold-formed Z-purlins with sloping lips is presented. The model is composed of the compressive lipped flange and part of the web, upon which two interactive springs are attached, representing the restraints of remaining part of the cross section. The...

The buckling of parallel purlins/girts is presented with attention paid to the effectiveness of the sag rods. Buckling of a simply supported purlin/girt with two sag rods at the one-third point along the span is studied. The lateral displacement of the upper flange is prohibited and distributed torsional restraints are provided to the purlin/girt b...

This paper studies the minimum stiffness required to ensure elastic buckling and elastic-plastic post-buckling strength of subpanels of vertically stiffened steel plate walls (S-SPWs) under compression. In the linear elastic analysis, the threshold stiffness at which the buckling mode of S-SPWs changes from overall to subpanel local buckling is det...

A curvature ductility-based nonlinear dynamic analysis procedure was developed to analyze the seismic force reduction factor of flexure-type building. A nominal height of base shear was defined to provide an effective link between base shear and base moment for multi-story flexure-type building. Two site-specific characteristic periods were utilize...

Buckling of purlins, supporting standing seam roof, simply supported at both ends and acted by pure moment, is studied by a closed-form solution. The uniform distributed torsional restraint provided by the roof sheeting and the lateral elastic restraint provided by the sag-rod placed at the mid-span are considered. The analytical solutions are foun...

To study the fire performances of the simply supported fire-resistant steel-concrete composite beams (FRSCCB), the simply supported FRSCCB with fireproof coating and fire-proof board under standard fire were simulated by the finite element (FE) software ABAQUS. The effects of the load-ratio, the fire-insulation of the steel beam, the strength of ma...

The fire performances of FRSCCB at both steady and transient state were analyzed based on the high-temperature mechanical properties of the Q345 fire-resistant steel produced by the Wuyang Iron and Steel Co. Ltd. in order to analyze the fire resistance time and the bending bearing capacity of fire-resistant steel-concrete composite beams (FRSCCB)....

This article reports a theoretical study on shear yielding and ultimate shear capacities of anchor bolts. Two theoretical models are provided. The proposed shear yielding capacity is a summation of that provided by bending of the anchor bolt itself and the frictional force on the interface between the base plate and concrete. A free length of the b...

In this paper, a theory is developed for analysis of steel-concrete composite beams with interfacial slip and shear deformation in steel considered. Closed-form solutions are derived for simply supported composite beam under uniform and mid-span concentrated load respectively. Examples are given to compute various quantities of beams. Comparing the...

A unified model for the distortional and lateral buckling of cold-formed Z-purlins subjected to bending is proposed in this paper. The model can study both the distortional buckling and the global buckling. The new model is different from Hancock's model. Two interactive springs between lateral and rotational restraints were introduced in this mode...

Simply supported purlins inter braced by one line of sagrods in a parallel purlin system under wind suction are analyzed. The sagrods are assumed to be zigzag placed with 30–50 mm offset in adjacent spacing. The effect of this offset and the local deformation on the effectiveness of sagrod is analyzed. A purlin is divided into 3 segments by offsett...

In the paper the buckling of simply supported plates under combined bending, shear and patch loading is studied in this paper with ANSYS, such a stress state occurs in girder supporting over-head crane. The effect of the width-to-height ratio of the plate and the width of patch loading on the interactive curves are analyzed in detail. And, it is fo...

Fire resistance tests were carried out on 2 fire-resistant steel-concrete composite beams (FRSCCB)with different thicknesses of fire fireproof coating, and 1 conventional structural steel-concrete composite beam(CSSCCB) under the same conditions as a control group. The furnace temperature, the temperature distribution along the composite beam secti...

The buckling of plates with two one-sided stiffeners arranged symmetrically under uniform compression was analyzed to determine the effective stiffness of one-side stiffeners. Second order analyses were conducted for the isolated stiffener and the plate acted by their interactive forces, and they are combined to satisfy the continuity conditions in...

Anti-sag bar is frequently adopted to enhance the lateral stiffness of cold-formed steel purlins. In existing studies, the anti-sag bar is normally treated as the rigid lateral restraint of cold-formed steel purlins, while according to the previous study of the authors', the local deformation of purlin web near the location connecting the anti-sag...

Lateral buckling is a main failure mode controlling the strength of C- and Z-section purlins under wind suction, as the compressive flange of cross-section is laterally free in this case. The lateral buckling of roof purlins is different from the normally considered simply supported beams, because the top flange of cross-section of these purlins is...

Fire protection thickness of CFT of FR steel was analyzed under certain fire resistances To obtain fireproof performance of concrete-filled steel tube(CFT) of fire-resistant(FR) steel in the fire. Fireproof retardant coating, cement mortar were used as fire protection for CFT of FR steel with circular cross section. And autoclaved aerated concrete...

This paper reports an investigation into the stability of dual systems composed of the multi-storey steel frame and the flexural-shear bracing system. The lateral buckling of cantilever column, to simulate the bracing system in the dual systems, is first studied with both the flexural and shear deformations taken into account. A very accurate solut...

The elastic buckling analysis of steel shear walls stiffened by vertical tubes under non-uniform compression is carried out using FEM, and the curves relating compressive buckling stresses to the rigidities of stiffeners are obtained, from which the threshold rigidities of the stiffener are obtained, which are the demarcation of global buckling and...

The effective bending stiffness of one-sided stiffener in reinforced steel shear wall was analyzed. The stiffener and the plate were isolated and acted by their interactive forces along the connecting line. The plate was analyzed as loaded by in-plane and out-plane loads. The stiffener was analyzed as simply supported beam. The plate and the sitffe...

This paper developed a unified model for the distortional and lateral buckling of cold-formed C-purlins subjected to bending in the plane of symmetry. It can study not only the distortional buckling, but also the global lateral buckling. Different from Hancock's model, the new model includes two interactive springs between lateral and rotational re...

The anti-sag bar is frequently adopted as an effective solution to enhance the lateral stiffness of cold-formed steel purlins. In many existing methods (e.g. EC3 method), the anti-sag bar is treated as the rigid lateral bracing for cold-formed steel purlins, which may overestimate its bracing efficiency due to the local deformation of purlin web ne...

To know about fireproof performances of concrete filled tubes(CFT) of fire-resistant(FR) steel with circular cross-section, the temperature field of CFT of ordinary steel under the fire heating curves was simulated using ANSYS. The fire resistance and load-bearing capacity of CFT of FR steel were solved with numerical technique under different diam...

Based on the buckling theory of thin-walled members and the total potentials of cold-formed Z and C purlins whose lateral restraints are ignored, the formulae of rotation and lateral displacement of the purlins were obtained under wind suction on the principle of variation. Considering the nonlinear strain energy generated during flexural-torsional...

An experiment program mainly about 28 groups of profiled corrugated steel sheets is introduced. By changing thickness of roofing board, thickness of purlin, height of purlin web and shape of clips for standing seam roof panel, the total torsional rigidity and factors that affect the total torsional rigidity were obtained. The torsional rigidity off...

The dynamic elastic-plastic analysis of systems of bilinear elastic (BIL) model and shear-slipped elastic-plastic (SSP) model was conducted to acquire the seismic force modification factor R for different site and ductility. The R-spectra were constructed with their abscissa normalized with two characteristic periods. The R-spectra with the dynamic...

A chevron bracing structural system is widely used in multi-story and high rise steel constructions. While under severe seismic actions, a significant unbalance force in the vertical direction may form at the intersect point of the braces due to the buckling of the compressive brace. This unbalance force, acting at the mid-span of a beam, may lead...

To investigate the post-buckling strength of the compressive brace in the chevron braced frame, the strength of the moment-resisting frame to the behavior of the dual structural system and the lateral load carrying capacity of the dual structural system, a series of nonlinear finite element analysis were conducted on the dual structural system usin...

This paper presents an analysis of the seismic force modification factor R of single degree of freedom system including strength degrading modified elastic-perfectly plastic (MEPP) model, bilinear elastic (BIL) model and shear-slipped elastic-plastic (SSP) model for different site and ductility factors. Results reveal that the strength degradation...

The elastic-plastic analyses were carried out for 50 moment resisting-chevron braced frames with weak beams for braced frame, in which the brace of out-of-plane slenderness between 30 and 150 and the moment-resisting frames with lateral resistance being respectively 25% and 50% of the total base shear are adopted. The results showed that the relati...

This paper investigates the deformation of compressed bars with I-section. A finite-element program of 3D-Steel-Struct developed by authors is used in the analysis. Initial geometric crookedness, residual stress and material inelasticity are considered in the investigation. Second order elastic and second order rigid-plastic analysis are carried ou...

Micro-sized silver power was prepared from AgNO 3 power by chemical reduction, and the technique was optimized by orthogonal experiment. The silver sol was obtained from silver nitrate via chemical reduction in ultrasonic wave and alkaline environment using polyethylene glycol (PEG-10000) as dispersant and alcohol as antifoam agent, and after agita...

The elastic-plastic analysis was made for chevron-braced frames with strong beams, the slenderness and inclination of a brace are varied and the beams are strengthened with four different levels. The results showed that strong beams can delay the degradation of the compressed brace's strength and allow the tensile brace yield, leading to the chevro...

This paper reports an experimental study on shear behavior of anchor bolt connection at column bases. Totally 15 specimens in 5 groups were tested where the bolt diameter, the thickness of base plates and difference between diameters of the bolt hole at base plate and bolt were varied. The load-slip curves typically show two characteristic loads, r...

Rectangular hollow section (RHS) is widely used as columns of agricultural greenhouse constructions. To enhance the resistance of these columns against the out-of-plane buckling failure, the bracing system is frequently adopted, typically composed of the bracing spans containing a two-layer x-brace at intervals of a number of spans and a horizontal...

This paper analyzed seismic response of SDOF elastic-perfectly plastic (EPP) hysteretic systems considering P-Δ effect. It used totally 370 earthquake records belonging to four site and soil conditions to calculate the inelastic deformation ratios (C d) with different ductility, and used the characteristic periods T ga and T gR to normalize the C d...

The rigid joints between a rectangular hollow section (RHS) column and an I-beam are widely used in steel constructions. The warping transfer through these joints between the columns and beams is studied in this paper. Simply relationships are proposed, based on the previous work by the authors, and the method is developed for use of these relation...

In the overall stability analysis of thin-walled members employing the general purpose finite element (FE) softwares, the members are generally modelled using the thin-walled beam elements or the thin shell elements. The modelling details of these two FE models were presented, and a new thin shell element model, capable of prohibiting the local buc...

The flexural strength of a reinforced concrete, metallic or timber beam can be increased by bonding a thin plate, made of steel or fiber-reinforced polymer, to its tension face. A main failure mode of such plated beams involves debonding of the plate end from the beam and such plate-end debonding depends strongly on the interfacial stresses between...

Lei Zhang and Geng Shu Tong thanked all the researchers who had presented their views on their paper on elastic flexural torsional buckling of thin-walled cantilevers. The two researchers discussed the equations and techniques that were employed in preparing the research paper on the topic. They informed that some challenges were faced in describin...

The strength or stiffness of a reinforced concrete (RC), metallic or timber member can be increased by bonding a thin FRP or steel plate to its external surface. In such plated members, debonding of the thin plate from the original member is often the controlling failure mode, and such debonding depends strongly on the interfacial stresses in the a...

This paper first briefly reviews the modified effective length method in the literature for design of steel columns considering the inter-column interaction with the limitations outlined. To overcome these limitations, a new storey-buckling approach for steel frames is presented, where each storey is treated as a whole at the sway buckling, and its...

This paper presents a new theory for the lateral buckling of web-tapered I-beams. Linear analysis is first conducted by taking account into the tapering effects of web-tapered I-beams, where the deformation compatibilities of the two flanges and web are considered in terms of the basic assumptions of thin-walled members. Subsequently, the total pot...

A fast FRP strengthening technique for steel structures that employs FRP prepregs (including two types of CFRP prepregs with different elastic moduli and a GFRP prepreg) and film adhesive is presented. Depending on the curing temperature, with this technique, the entire strengthening process may take only a few hours. The tensile test results of do...

This paper reports an experimental investigation on the structural behavior of lapped connections over the internal supports in multi-span cold-formed steel Z purlin systems. The moment resistance and effective flexural rigidity of two typical connection configurations, i.e. web bolts plus self-drilling screws at both flanges or at the top flange o...

Previous studies by the authors revealed that the two representative theories with slight differences between, widely used in investigating the flexural-torsional buckling of thin-walled beams, have led to two different solutions in well-known literature for assessing critical loads of simply supported beams of monosymmetric cross section. With the...

The use of FRP (Fibre Reinforced Polymer) to strengthen steel structures has become an attractive option which may produce confident retrofitting of existing structures. This paper reviews the following areas that have received only small coverage in previous review articles, but have developed rapidly: the bond between steel and FRP, the strengthe...

This paper investigates the buckling of thin-walled beams braced by horizontal knee angles, which is a new practice currently coming into use in Chinese industrial buildings with small and moderate overhead cranes of light or medium duty to improve the stability of simply supported crane runway girders. It was found that this technique increases si...

The use of steel plates or externally bonded fibre-reinforced polymer laminates for flexural strengthening of concrete, masonry, timber or metallic structures is a technique that has become very popular. The effectiveness of this technique hinges heavily on the performance of the bond between the strengthening plate and the substrate, which has bee...

Generally, it is relatively easy to obtain a high joint strength with most modern bonding systems if these are cured under ideal factory conditions. However, civil engineering construction joints are cured on site and are required to last the lifetime of the structural member in harsh environmental conditions. This implies that site joints might no...

For beam-to-column rigid joints with a diagonal stiffener, the warping degrees of freedom at the beam-to-column joint have been taken to be continuous in some current literature. A new warping transmission model is presented for this type of joint in this paper, in which the bending deformation and twisting of the diagonal stiffener are considered...

This paper reports an experimental investigation on the bending behavior of cold-formed continuous Z-purlins with lapped connections. The first part of the tests was performed on the load-carrying capacity of the lapped segments. The specimens are simply supported beams with cantilevers of the same span length, and concentrated loads applied at the...

The elastic stability of two span continuous beams has been studied using FEA methods. Two formulae for estimating the critical loads are proposed, one is suitable for two-span beams with one span loaded, while the other is suitable for two-span beams with both spans equally loaded. Two identical concentrated loads symmetrically located about the m...

This paper summarized currently available techniques of setting up flexural–torsional buckling theory of thin-walled members. It is found that all the existing methods introduced a nonlinear load potential in their total potentials, while based on the classical variational principle for stability of a solid structure, no such load potential should...

This paper investigates elastic buckling of inter-braced parallel beams when beams are not equally loaded. For beams under uniform bending, analytical solutions and approximate solutions using the Rayleigh-Ritz method are obtained respectively, and it is found that they agree with the exact solutions excellently. The Rayleigh-Ritz method is further...

There are two different formulae available for calculating the critical moments of thin-walled beams under transverse loads. They give quite different results for beams with monosymmetrical cross-sections. This paper reviews the stability theories for thin-walled beams and identifies some points which might be present and have led to the current si...

There exists two different theories on the flexural-torsional instability of the thin-walled members, and based on them, very different results for beam elastic buckling can be obtained. In this paper, a new theory is presented to solve the inconsistency between the two different theories noted above after very deep investigation, In this new theor...

There exist two different theories on the flexural-torsional instability of the thin-walled members, and based on them, very different results for beam elastic buckling can be obtained. In this paper, a new theory was presented to solve the inconsistency between the two different theories noted above after very deep investigation. In this new theor...

Polyacetylene and polyaniline usually have one-dimensional character because their interchain coupling interaction is weak. As the pressure increases, the interaction also increases and interchain energy gap reduces so that interchain distance b decreases and interchain elastic distance increases. When b approaches the lattice constant a, the polym...

As the real trans-polyacetylene molecule has finite chain length, its chain-terminal effects on various properties should be taken into account, that is to say, the aperiodic boundary condition should be employed in studying the properties of conducting polymers. However, if trans-polyacetylene chain is long enough, the chain-terminal effects can b...

The transverse stresses are studied in thin-walled mono-symmetrical steel I beams. Equations are obtained to calculate these stresses in the three plates of the beam. The effect of these stresses on the beam strength has been analyzed. It is found that these transverse stresses in the flanges need to be considered carefully in strength checks at th...