Side Of Column Research Articles

Dynamic Response Analysis of RC Frame against Progressive Collapse Based on Orthogonal Test

We aimed to investigate the extent to which the initial state generated by unexpected loads, such as explosions and impacts on the remaining structure, affects the dynamic response of the structure. The study used the orthogonal test method to obtain orthogonal table L25 (53) by combining five levels of each of the three factors of column removal time and initial velocity, and the initial displacement of the remaining structure under three failure scenarios of the corner, side, and internal columns at the ground floor of the reinforced concrete frame structure. The degree of influence of different factors on the structural dynamic response, and the result of the unifactorial impact of initial velocity and initial displacement of the remaining structure on the structural dynamic response in the case of failure of the bottom side columns, were obtained by the polar difference method. The results show that the analysis using the orthogonal test polar difference method revealed that the initial displacement has a more significant influence on the dynamic response of the structure, forming the main influencing factor. At the same time, the failure time and initial velocity have a smaller influence on the dynamic response of the structure as secondary influencing factors. In the case of unifactorial influence, the initial upward displacement and initial upward velocity are detrimental to the structure, leading to progressive collapse. In contrast, the initial downward velocity and initial downward displacement are favorable.

Robustness of steel braced frame to resist disproportionate collapse caused by corner column removal

Steel braces have been widely used as a major lateral stability system to resist the lateral load. However, the influences of steel braces on enhancing the load resistance in moment-resisting steel frames under column removal have not been studied adequately due to the lack of experimental data, especially under worst case scenarios, corner column removal. Thus, five two-floor steel moment-resisting subframes with or without braces were tested by applying a pushdown force. The purpose of this study is to quantify the effects of steel braces on the robustness of steel moment-resisting frames against disproportionate collapse. The test results indicated that steel braces could enhance the ultimate load bearing capacity up by 102.3%. Compared to V configuration, X configuration is more efficient in increasing the load resistance since a proportion of the vertical load may be transferred to the side column through diagonal braces straightly. The de-composition of the load bearing capacity indicated that compressive braces only affect the initial stiffness and most of the load resistance is attributed to tensile braces for both X and V configurations. De-composition of the load bearing capacity indicated that the load bearing capacity from the first floor is normally greater than that from the second floor due to greater Vierendeel action mobilized.

Performance of RC beam-column assemblies during and after elevated temperature to resist progressive collapse

In practice, fire is one of the accidental loads that can result in the progressive collapse of buildings but the commonly used alternate load path (ALP) approach often ignores the impact of fire. Therefore, numerical models based on the finite element software ABAQUS are employed to investigate the performance of reinforced concrete (RC) beam-column assemblies during and after high temperature to resist progressive collapse. The thermal–mechanical sequential coupling method is used for analysis. The effects of fire durations, boundary conditions (middle or penultimate column removal) and side column subject to fire are studied. Previous test results demonstrated that compressive arch action (CAA) and catenary action (CA) are developed in sequence to prevent progressive collapse for the assemblies at ambient temperature. However, the numerical results show that the in-fire assemblies could not develop CA owing to severe degradation of rebar elongation and thus, the load resistance of in-fire assemblies controlled by CAA capacity. Further increasing fire duration to 90 mins, the CAA capacity of the assemblies decreases over 70% compared with that at ambient temperature. Since the rebar can recover most of its mechanical properties after cooling down, the assembly after fire (i.e., exposed to fire then cooled down) can also successively develop flexural action (FA), compressive arch action (CAA) and catenary action (CA) to resist progressive collapse, which is similar to that of intact RC frame at ambient temperature. Under the penultimate column removal scenario, the exterior side column of the post-fire specimen suffers large eccentric compression failure, which causes the highest collapse risk.

Seismic performance of rocking‐delayed spine frame system with base initial gaps

AbstractThis study proposes a rocking‐delayed spine frame system that provides initial gaps at the side column bases of the spine frame. This system exhibits a trade‐off behavior between the nonuplifting spine system and uplifting‐allowed rocking frame system. The feasibility of the proposed system was verified on 16 specimens using cyclic loading tests. An evaluation of the force–deformation relationship of the proposed system was proposed and verified by comparing it to the test results. The seismic performance of the proposed system was investigated using nonlinear time‐history analysis. The analysis results clarified the initial gap's influence on seismic responses. A trade‐off between the maximum story drift ratio, peak floor acceleration, and maximum shear force of the spine frame was revealed.

Evaluation of collapse resistance of masonry-infilled RC frame building under blast loadings

As non-structural members, the masonry-infilled (MI) walls are always ignored in the numerical and experimental study on the blast and collapse resistance of RC frame buildings, while the contribution of MI walls on preventing the large-scale collapse has been observed according to the past explosion incidents. This paper aims to propose and verify a numerical simulation approach considering the blast- and collapse-resistant effects of MI walls, and further evaluate the collapse resistance of MI RC frame buildings under blast loadings. Firstly, based on our previously validated hybrid finite element (FE) modelling approach for RC frame structures and Multi-material Arbitrary Lagrangian-Eulerian method for applying blast loadings, the simplified micro-model and compressive strut model of the MI wall were adopted to characterize its blast and collapse resistance in the near- and far-regions of building, respectively. Secondly, the out-of-plane explosion test and in-plane quasi-static collapse test were numerically reproduced to verify the applicability of adopted FE modelling approaches for MI walls. Furthermore, by establishing the hybrid FE models of prototype bare and MI RC frame buildings, the propagation of blast waves, damage modes as well as dynamic responses of RC frame buildings under two design-based threat of explosion at corner and side columns were derived and examined. Finally, the applicability of the anti-collapse design method specified by U.S. Department of Defense, i.e., alternate path method (APM), for RC frame buildings under external explosions was examined. It derives that, (i) the presence of MI walls can efficiently block the blast waves into the building structures, and relieve the upward arch of slabs and damage degree of interior columns; (ii) compared with the bare RC frame buildings, the MI walls provide sufficient alternate load paths to enhance the structural robustness and restore the gravity stability of MI RC frame buildings after the explosions; (iii) the APM is only applicable to evaluate the collapse resistance of MI RC frames under the external explosion of cargo van bomb (1814 kg of equivalent TNT) or even less charge weight.

Seismic performance analysis of adjacent eccentric structures based on PSO algorithm

Adjacent structures connected by dampers can effectively prevent collisions and attenuate the response of these structures. An early simplified model was investigated using a two-dimensional model. However, this model disregarded the effect of torsional response due to eccentricity. The eccentric arrangement of dampers owing to the non-parallel centroid between adjacent structures has not been considered in existing research. Here, the vibration equation of adjacent structures connected to a Kelvin damper was derived to study the torsional response under earthquake excitation. Furthermore, a PSO (Particle Swarm Optimization) algorithm was adopted to conduct a parametric study. Additionally, the damping effects of adjacent structures were compared using various damper layout schemes. The results show that the structural displacement was reduced by 50% by connecting dampers between adjacent structures. Placing dampers in the middle of a structure has a greater damping control effect than placing them on the side columns. However, the optimal damper layout must be chosen based on the diverse eccentric combinations and control goals of the adjacent structures. A damper can be arranged eccentrically to increase its damping control effect on an adjacent structures by 50% to 75%. The weakening of the edge effect on the damping effect should be considered when choosing the control objective for damper optimization. This weakening impact can reduce the damping effects by 50% and lead to greater deformation of the side column. The response of adjacent structures can be controlled macroscopically by utilizing the translation–torsional energy ratio as the control goal. However, a high fundamental frequency ratio of adjacent structures should be avoided.

Seismic behavior of a precast RC frame–shear wall structure using full/half grout sleeve connections

To investigate the seismic behavior of precast RC frame–shear wall structures using full/half grout sleeve connections, two RC frame–shear wall structure specimens were constructed and tested under cyclic loadings: the first specimen was a precast RC frame–shear wall structure (Specimen PCFW), and the second specimen was a conventional RC frame–shear wall structure (Specimen RCFW) cast in situ. The seismic performance of Specimens PCFW and RCFW including the failure modes, hysteretic responses, and energy dissipation capacities was investigated. Furthermore, the mechanical behavior of Specimen PCFW was numerically simulated using the OpenSees software. The test results show that the crack distribution of Specimen PCFW is more dispersed than that of Specimen RCFW. In particular, few cracks appear in the area of full/half grout sleeves in Specimen PCFW. However, the damage to the concrete around the half grout sleeves of the side columns in the shear wall of Specimen PCFW in the 1st story was more severe than that in the corresponding region of Specimen RCFW for a less thick concrete cover. Compared to Specimen RCFW, Specimen PCFW exhibits higher lateral bearing capacity, better energy dissipation ability, and slightly lower ductility. In addition, assuming the equivalent principle of rebar area, the mechanical behavior of Specimen PCFW can be effectively simulated using the nonlinear multilayer shell element in the OpenSees software.

Effect of openings on lateral behaviors of corrugated plate module walls and high-rise modular buildings

In modular buildings with container-like modules, the corrugated plates and the opening conditions were proven to have significant influence on the module rigidity. But the effect of openings on failure modes of modules and lateral sway performance of modular buildings were rarely considered. In this paper, shear performance of long modules with different kinds of openings and different beam sections were investigated. A simplified analytical model of perforated module sidewalls was proposed and was applied to the seismic structural analyses of high-rise modular frames. Results indicated that the opening subdivided the corrugated plate sidewalls, which mechanism led to the postponement of plate buckling and the increased elastic shear strengths comparing to intact walls. High stress concentrations and regional plate buckling firstly occurred around the opening, and then the buckled regions expanded toward two side columns as the increase of shear drifts. The frame beams and regional corrugated plates above or below the opening behaved like a kind of coupling beams that channeled short corrugated sidewalls at two sides of the opening. The bending rigidity of the coupling beam system determined the composition effect of short corrugated plates at two sides of the opening, and then directly influenced the drift performance of individual modules and the whole modular buildings.

A CFD Study of Vortex-Induced Motions of a Semi-Submersible Floating Offshore Wind Turbine

Vortex-induced motion (VIM) is a critical issue for floating structures made of one or more columns, due to its significant impacts on their operational stability. Supported by column-type floating platforms, floating offshore wind turbines (FOWTs) may also experience large-amplitude VIM responses in current flow. Existing research on FOWTs has mostly focused on their wind/wave induced responses, yet less attention has been paid to their responses in current flow. In this paper, the VIM of the OC4 semi-submersible FOWT platform is studied numerically over a wide range of flow velocity. Three incidence angles, i.e., 0°, 90°, and 180°, are considered and the effect of current incidence on platform VIM is analysed. Results show that the so-called lock-in phenomenon is present and that a large transverse response amplitude of more than 0.3D persists until Vr = 30, with its maximum reaching over 0.8D at Vr = 8. Meanwhile, the transverse response amplitude for cases with the incidence angle of 180° is generally smaller, with a narrower lock-in regime, than those under the other two incidence scenarios. Flow field visualisation reveals that upstream vortices continuously interact with the downstream side column when the incidence angle turns to 180°, impacting the vortex shedding process and consequently fluid forces of the downstream column.

Seismic behavior of steel plate and reinforced concrete composite wall coupled to steel side columns

The steel plate and reinforced concrete (SPRC) composite wall coupled to steel side columns is a new type of coupled system, which consists of a single SPRC composite wall coupled to steel side columns through steel coupling beams at all floors. One 1/4 scaled five-story SPRC composite wall coupled to steel side columns with a plastic coupling ratio (CR) of 0.45 was designed, constructed, and tested under simulated earthquake action. The test results exhibited great seismic performance of the proposed coupled system with the coupling mechanism fully developed. The average displacement ductility coefficient was 3.12. And the average values of the inter-story drift ratio of all stories at the yield, peak load, and ultimate conditions were 1.32%, 2.55%, and 3.70%, respectively, showing good inter-story deformation capacity. The average ultimate plastic shear rotations of steel coupling beams at the 2nd, 3rd, 4th, and 5th floors were 0.0211 rad, 0.0364 rad, 0.0556 rad, and 0.0913 rad, respectively, indicating great energy dissipation contributions of the steel coupling beams. The steel side columns remained elastic under shear forces transmitted from steel coupling beams through hinge joints and provided a stable overturning moment resistance to protect the SPRC wall. The accuracy of the test results was verified against the numerical analysis results. The parametric analyses were conducted to further the understanding on the influences of key design parameters on the seismic performance of the proposed coupled system. The peak lateral load can be enhanced by increasing the axial load or steel plate ratio. In order to obtain good energy dissipation capacity and ductility, a moderate value of 0.15 for the axial load ratio or 6.6% for the steel plate ratio can lead to excellent deformation capacity.

Experimental and Numerical Study on Progressive Collapse Analysis of a Glulam Frame Structure: I. Side Column Exposed to Fire

This paper presents experimental and numerical investigations on progressive collapse behavior of a two-story glulam frame when the side column is exposed to ISO834 standard fire. The collapse mechanism initiated by fire is identified. The experimental results show that the progressive collapse of a glulam frame could be described for three stages, namely bending effect stage, catenary effect stage and failure stage, respectively. These stages are discussed in detail to understand the structural behavior before and during collapse. It is demonstrated that the entire frame slopes towards the side of the heated column, and the “overturning” collapse occurs eventually. The catenary effect of beams is the main reason for the progressive collapse of the frame. In addition, a finite element model of a glulam frame is established to simulate the progressive collapse behavior. The effects of axial loads on the columns are summarized. The numerical simulation results agree well with the experimental results, which could verify the effectiveness and practicability of finite element simulation. Furthermore, the progressive collapse resistance of the frame in practical design were proposed.

Preliminary analyses of an innovative solution for reducing seismic damage in steel-concrete hybrid-coupled walls

Hybrid steel-concrete structures used as earthquake-resistant systems are an interesting solution for buildings in seismic prone areas, combining in effective ways the benefits of concrete and steel. In this context, an innovative single-pier hybrid coupled wall (SP-HCW), made of a single reinforced concrete wall coupled to two steel side columns by means of steel link, was recently proposed. The system is conceived to reduce the damage in the reinforced concrete wall while concentrating dissipation to the replaceable links. Although the numerical analyses for this innovative solution showed encouraging seismic performances and the desired ductile global behaviour, bottom zones of the concrete wall might experience undesired damages. Starting from the first proposed SP-HCW, in this study a new solution for its base is presented and preliminary investigated, i.e., the wall is designed as pinned at the base and equipped with additional vertical dissipative devices. In this way, this new configuration is expected to achieve lower damage of the wall without reducing its dissipative capacity. In this article the results of preliminary pushover analyses are discussed to evaluate the expected performances of the proposed structural solution.

BEHAVIOR OF MAT FOUNDATION FOR A TEN-STORY BUILDING: FIXED BASE VS THREE-DIMENSIONAL SOIL MODEL

Soil is an anisotropic, heterogeneous, and inelastic complex material. It is difficult to represent the exact behavior of soil by numerical modelling in practice. Conventionally, soil is simplified to an idealized model where it is considered isotropic, homogeneous, and behaves elastically under loads. The idealization, in this case, is done using the proper elastic modulus, Poisson’s ratio, and unit weight of soil depending upon the soil type. Although the exact soil behavior is simplified, using Finite Element Analysis (FEA) a more effective result can be obtained. A superstructure was modelled using ETABS using a fixed-base system and the base reaction forces were obtained. A mat and a soil element on which the mat was laid were modelled as a flexible-base system in Midas GTS NX. The base reactions obtained from ETABS were applied to the mat in the soil model to determine the settlements and, consequently, the spring stiffness. The superstructure was then modelled again, incorporating springs under the respective columns. Convergence in settlement, and base reactions were reached by iteration, and the final results from the flexible-base system were then compared with the fixedbase system. The center column settled the most, about 60 mm, and there was a decrease in settlement by 15% between the first model and the final iterated model. The base reaction for center columns decreased by 24% in the flexible base system compared to the fixed base system. However, an increase in base reaction was observed for both side and edge columns. There was an extremely erratic change in grade beams under a flexible base system, which shows that the superstructure elements are also affected by the change in the base system. It is recommended to use this approach, for the analysis of structures considering flexible base systems instead of fixed bases because it enhances the accuracy of analysis with feasible time consumption and less complex effort.

Correlation Research between Asymmetry Coefficient of Gondola Car Body and Stress Distribution of Cross Bearer Weld

In order to find out the root cause of cross bearer welds’ cracks in general-purpose gondola cars, the relationship between asymmetric structure and stress distribution is studied in this paper. Firstly, the concept of asymmetry coefficient and stress distribution cluster is proposed, and the asymmetric coefficients’ calculation methods of independent and dependent variables are given, respectively, in two-dimensional space. Secondly, according to the different positions of side column 1 and side column 2, 30 local models are established, the cross bearer weld stresses are extracted after finite element simulation, and the stress distribution clusters of cross bearer weld stresses are formed. Finally, the asymmetry coefficients of the side columns are calculated, and the correlation between the positions of the side columns and the weld stresses is studied using the methods of Pearson correlation coefficient and complex correlation coefficient. The results show that the correlation between the stress of cross bearer weld 2 and the positions of the side columns is much higher than that between the stress of cross bearer weld 1 and the positions of the side columns. Meanwhile, it shows that the method presented in this paper is feasible and effective for the analysis and research of asymmetric structures. These combined with the calculation method of the correlation coefficient.

Experimental study on seismic performance of modular steel construction beam-to-beam combined side column joint with blind bolted connection

With the increase in the construction height of modular structures, the challenge of structural seismic resistance is increasing, and the performance of joints between modules is the key to the seismic performance of modular structures. This paper proposed a modular steel construction beam-to-beam combined joint with blind bolted connection. To study its seismic performance, quasi-static tests on four full-scale T-shaped joints with different construction forms were conducted, and the failure mode, strength, stiffness, ductility, and energy dissipation of the joints were obtained. The results showed that the joint had good seismic performance, and the performance of the enhanced joint was significantly improved after blind bolts and stiffening plates were used. Furthermore, based on the test results, the simplified mechanical model of the joint was established. The calculation method of joint stiffness and bearing capacity was obtained by theoretical derivation, and the design method of the joint was proposed. The analysis showed that the calculated results were close to the experimental results, and the proposed enhanced joint could meet the requirements of rigid connection and full-strength connection joint.

Seismic analysis and connection optimization of the side column on modular prefabricated four‐sided connected composite shear wall

SummaryA modular prefabricated four‐side connected composite (MPFC) shear wall that consists of a composite shear wall modular (CSWM) and steel frame boundary elements is proposed. First, the finite element model (FEM) of the MPFC shear wall, which considers a plastic‐damage constitutive model of both concrete and steel materials, is established based on the finite‐element software ABAQUS. Second, the FEM accuracy of the MPFC shear wall is verified by the experimental results of a modular prefabricated two‐sided connected buckling‐restrained (MTB) steel plate shear wall. Third, the seismic performance of the MPFC shear wall is investigated based on the verified FEM. The connection between the CSWM and side column is optimized. Finally, the initial stiffness calculation formula of the MPFC shear wall that considers the impact of that the thickness ratio between the connection steel plate (CSP) and inner steel plate (ISP) is deduced. The results show that the peak bearing capacity, initial stiffness, total energy, and total strain energy of the MPFC shear wall increased by 42.47%, 44.81%, 113.24%, and 58.97%, respectively, compared with those of the MTB steel plate shear wall. The compressive corner damage of the reinforcement concrete faceplate (RCF) of the MPFC shear wall with a side column and CSWM is connected by a middle steel plate is effectively improved. Compared with those of the MPFC shear wall in which the side column and CSWM are connected by bolts, the shearing force, axial force, and bending moment of the side column of the MPFC shear wall in which the side column and CSWM are connected by the middle steel plate are notably decreased by 25.32%, 26.08%, and 39.51%, respectively. The FEM results are compared with the formula calculation results to establish its accuracy in calculating the initial stiffness of the MPFC shear wall.

Numerical Simulation Study of Progressive Collapse of Reinforced Concrete Frames with Masonry Infill Walls under Blast Loading

The influence of masonry infill walls on the progressive collapse performance of reinforced concrete (RC) frame structures was investigated in this paper, using a nonlinear dynamic analysis approach. Based on ANSYS/LS-DYNA finite element software, two finite element models of RC frame structures with and without masonry infilled walls were established. Then, the collapse modes of the two RC frame structure models were analyzed for different scaled distance blast loads, different locations of column damage, and different span numbers. The results show that with the increase of explosive amount, the collapse degree of the structure is more serious in the same time. Under the condition of destroying the outermost central column, the degree of progressive collapse of the RC frame model with infilled walls in the same time is lower than that of the RC frame model without infilled walls. The RC frame model with infilled walls is more resistant to collapse when the outermost side columns are damaged. With the increase of span number, the structure is more likely to be damaged and collapsed.

Novel method for designing and optimising the floating platforms of offshore wind turbines

Platform stability is a fundamental requirement for floating offshore wind turbines (FOWTs). In this paper, a novel method for designing and optimising FOWT platforms is proposed based on the design concepts of semi-submersible and spar platforms. The method involves developing an integrated numerical model of the FOWT by considering the fully coupled effect. Therefore, a new fully submersible FOWT platform with inclined side columns is parametrically designed based on the parameters of the NREL 5 MW wind turbine. The superiority of the new fully submersible FOWT platform is verified by comparing the material cost and dynamic response of two typical floating platforms. In addition, the design principles of additional structures and the mooring system of the floating platform are systematically analysed. The positive results verify the proposed method, which has greater hydrodynamic performance and economic feasibility compared with traditional semi-submersible and spar platforms. The enhanced hydrodynamic performance of the platform also improves the dynamic response of the tower and platform. The design of additional structures and mooring systems for floating platforms must consider structural safety and economic feasibility. The findings reported in this paper provide new insights into offshore wind exploitation in deep water with a feasible novel platform for FOWTs.

Collapse resistance analysis of composite beam–column substructure considering the location of column failure

In actual situations, it is not possible to determine the exact location where the column will fail (in a member or building structure). Based on the location of the failure, the lateral constraint stiffness of the directly affected area of the structure will change, affecting the structure's anti-collapse performance. This study aims to explore how the location of the failure column affects the collapse resistance of composite beam–column substructures; the double-sided restraint substructure (DSRS) and the single-sided restraint substructure (SSRS) were chosen as research objects, and the two test structures were subjected to static loading tests to compare their collapse resistance. The results showed that the two specimens had similar failure modes and deformation patterns. In addition, the development trend of the internal force of the two specimens was comparable, but the axial force of the SSRS was smaller. The contribution of the catenary mechanism of DSRS was approximately 24%, while the catenary effect of SSRS was not fully exerted, leading to only 15% of the total resistance. Two specimens were modeled in ABAQUS, and the finite element method was verified by comparing the simulation results with the test results. A full-scale model was established to analyze the effects of the lateral restraint stiffness of DSRS and SSRS and the side column size on the collapse resistance of the substructure. The finite element analysis results are as follows: (1) lateral restraint stiffness had less influence on the small deformation stage of the substructure; (2) the beam end tension force played a significant role in the collapse resistance of the substructure; (3) increasing the horizontal lateral restraint stiffness can effectively improve the anti-collapse performance of composite beam–column substructure; (4) the side column can provide effective axial and rotational restraint for the beam end. Having too large or too small a side column can have an adverse effect on the structure. Moreover, the larger the side column size, the better the continuous collapse resistance of the substructure when the beam–column linear stiffness ratio is between 0.6 and 1.1.

Experimental and numerical study on innovated steel Shear Resisting Frame with Haunched Beams (SRFHBs)

Steel shear panels are one of the most significant lateral resisting systems with high ductility and energy dissipation capacity. This paper describes and discusses innovated steel Shear Resisting Frame with Haunched Beams (SRFHBs) with a particular focus on very short link beams. Regarding shear panels performance, the conception of SRFHB emerged with the aim of improving the link beam behavior in Eccentric Bracing Frames (EBFs) as well as architectural constraints and overcoming the span-to-depth ratio limitation provided by the seismic provisions in Moment Resisting Frames (MRFs) which notified especially in tall buildings with framed-tube structural system. SRFHB is comprised of two strong side columns connected to the link beam as the shear fuse in the middle of the span through haunched beams. Application of the haunched configuration makes it comfortable to reach very short links. Shear fuse plays the governing behavior as sacrificing element to keep adjacent members safe. Shear yielding and out-of-plane deformations due to the tension-field action, control the amount of energy dissipation. An experimental program and extensive nonlinear dynamic analyses were conducted to validate the test results and evaluate the seismic behavior of the proposed system and idea in comparison of the conventional EBF. Results indicated that SRFHBs could develop considerable performance with more desirable seismic response than traditional EBFs.