Pushover Test Research Articles

Experimental study on seismic behaviour of composite frames with wide floor slabs considering the effect of floor loads

The steel–concrete composite frame systems are widely used in multistory and high-rise buildings owing to good mechanical performance and high construction efficiency. In previous research on the composite frame systems, many lateral cyclic tests were conducted on specimens with small-width floor slabs without floor loads, which could not precisely reflect the actual behaviour of composite frames in spatial multistory buildings. Therefore, this paper presents an experimental study on the seismic behaviour of composite frames with wide floor slabs considering the effect of floor loads. The specimen was a two-story two-span composite frame with the scale ratio of 0.5, and three load cases, including the vertical floor loading test, the lateral cyclic loading test and the pushover test, were respectively applied to investigate the mechanical performance of the composite frame. The slab crack development, mid-span deflection and strain distribution of slab reinforcements in the vertical floor loading test were discussed. The overall responses of the specimen in the lateral cyclic loading test and pushover test were analysed, including failure phenomena, load–displacement curves, strength and stiffness degradation, energy dissipation capacity and deformation characteristics. Moreover, the seismic performance of columns, beams, slabs and joints in the specimen was discussed in detail and the force mechanism of the composite frame was revealed based on the structural analysis of components. The results indicated that the specimen exhibited sufficient load-bearing capacity, good ductility, stable strength and stiffness degradation and excellent energy dissipation capacity under the combination of vertical floor loads and lateral loads. The welds at the bottom flange near the exterior joint fractured under cyclic loading, which was found to have significant influence on the deformation pattern and force mechanism of the composite frame. The shear lag effect was obvious in the wide floor slabs and the effective width of the slabs was estimated to be nearly 0.75 times the column width.

Centrifuge modeling of disconnected piled raft using vertical pushover tests

A disconnected piled raft (DPR) foundation has been introduced as an effective pile design to reduce the vertical loading experienced by the pile. The characterization of DPRs has focused on the load transfer mechanism, foundation and soil settlement, bearing capacity, load distribution, and bending moment of the piles. DPR piles can act to increase the bearing capacity of the ground, and DPRs can reduce settlement while securing the bearing capacity. In this study, centrifuge model tests are performed to simulate the static behavior of DPRs under actual stress conditions. The behaviors of the DPR foundation for axial load, axial load distribution among the piles, and bending moment are compared to those of the connected piled raft foundation to understand the complex behaviors of DPRs. The centrifuge test results show that DPRs help reduce the pile axial load and bending moment during vertical loading. In addition, DPRs show smaller vertical settlement than shallow foundations. Therefore, we confirm that DPRs can be applied in foundation design as settlement reducers.

Design and Verification Test of Quasi-Static Pushover Model Container

Laboratorial testing methods for exploring seismic response mechanism of underground structures usually consist of conventional shaking table test and centrifuge shaking table test. The types of model containers employed to investigate the seismic response mechanism of underground structures during dynamic tests include rigid, flexible and laminar shear model containers, all of them have some drawbacks. It is essential to choose an appropriate model container in terms of test requirement, according to the quasi-static pushover testing method a novel model container was proposed. A set of quasi-static pushover tests were conducted to verify the performance of the new container. The experimental results show that the designed model container can effectively simulate the most unfavourable deformation mode of invert triangle in push direction, which means that quasi-static testing method with this model container can be applied to evaluate seismic response of underground structures, furthermore, the deep-buried condition is also can be simulated.

The Push-Over Test and Numerical Analysis Study on the Mechanical Behavior of the GFRP Frame for Sustainable Prefabricated Houses

The glass fiber reinforced plastics (GFRP) composite material is a low carbon emission, low life cycle cost, and sustainable material. In this paper, the structural behavior of the lateral force resistant performance of GFRP composite material frames with steel joints was presented, and the energy dissipation and failure modes of the GFRP frames were discussed. A total of six GFRP frames, including single-span and double-span frames with and without diagonal bracing members, were tested by pushover tests to obtain the lateral load-displacement relationships of the GFRP frames. The force-displacement relationship and the energy dissipation of the GFRP frames were examined in the pushover test. In addition, the numerical analysis was performed to obtain the lateral load-displacement relationships of the GFRP frames under pushover tests. When the numerical analysis results and the experimental results were compared, the absolute average errors of the maximum loads were less than 4%, and the lateral load-displacement relationships were close to each other. The numerical analysis results can predict the experimental force-displacement relationships of the GFRP frames.

A damaging block-based model for the analysis of the cyclic behaviour of full-scale masonry structures

In this paper, a damaging block-based model is proposed for the numerical analysis of the cyclic behaviour of full-scale masonry structures. Solid 3D finite elements governed by a plastic-damage constitutive law in tension and compression are used to model the blocks, while a cohesive-frictional contact-based formulation is developed to simulate their cyclic interaction. The use of tests on small-scale specimens to calibrate the mechanical properties of the numerical model is presented and discussed. The tests belong to a comprehensive experimental campaign performed on calcium silicate brick masonry. The calibrated models are used to simulate in-plane and out-of-plane cyclic tests on masonry walls made of the same material, as well as a quasi-static cyclic pushover test on a full-scale terraced masonry house. The efficiency, the potentialities and the accuracy of the model here proposed are shown and discussed. The capability of explicitly representing structural details (e.g. running bonds) and any in-plane and through-thickness texture of masonry, which appears essential to study the response of masonry structures, is guaranteed by the block-based modelling approach. A good agreement between the numerical results and the experimental outcomes is observed. This allows to validate the model in the cyclic response as well as the strategy proposed for its mechanical characterization.

DUCTILITY OF REINFORCED CONCRETE SUB FRAME FOR INDUSTRIALIZED BUILDING SYSTEM

An accurate determination of industrialized building system (IBS) frames ductility under alternating lateral loads is the key issue of this study. The performance features of IBS H frame assembly subjected to cyclic lateral pushover test with six attached IBS components are reported. A test scheme of nonlinear elastic sub-frame system is proposed to build an IBS structural building system. This system complies with the requirements of strength and ductility governed by European Codes 2 and 8. The three models are a conventional reinforced concrete H frame system CRCH (Model 1), IBS with steel conventional links as reinforcements IBSHN (Model 2), and special spiral links concrete IBSHS (Model 3). Each model is scaled to 1:5. All models are laboratory examined under cyclic lateral pushover test to failure, where the IBS connections are considered as hybrid partial rigid linking beams to columns. The beam ends are connected to column boxes via a U shaped steel plate. The experimental results of the IBS specimens are compared with the conventional reinforced concrete connection of similar shapes and size in the form of H sub-frame mechanism tested under the same condition. The models are subjected to cyclic lateral load controlled applied at the beam-column connection. The performance evaluation of IBS connections is made via load displacement hysteresis, ultimate and collapse parameter, ductility index, and surface cracks appearances. The conventional concrete specimen is obviously found to display better strength compared to IBS. Conversely, the ductility of IBS H frame specimen with spiral shear links and conventional closed loop links exhibits superior features compared to the conventional concrete specimen which is beneficial to earthquake engineering. It is demonstrated that the performance of the precast concrete structure is highly dependent on the ductile capacity of connectors to each of the IBS component. This is significant especially at the joints such as the beam-to-column connections. Our systematic methods on ductility characterizations of reinforced concrete beams may contribute toward the development of IBS in resisting earthquakes.

Experiment-based reliability analysis of structural joints in a steel lattice tower

The main aim of this paper is to present a reliability estimation procedure for steel lattice telecommunication towers based on tensioned joint reliability. The experiment, which involved doing a full-scale pushover test of a 40 m high lattice tower, constituted the starting point for further analyses. Experimental data served as bases for finite element model calibration and assignment of steel mechanical properties based on tensile tests. A computational investigation was performed for random wind loads. Numerical considerations included a detailed dynamic analysis with respect to the specific wind velocity–time function, modeling of two particular tower joints by shell finite elements, and elastic-plastic range determination of joint reliability using the first-order and second-order reliability methods.

Collapse analysis of wind turbine tower under the coupled effects of wind and near‐field earthquake

AbstractIn this paper, the pattern of wind turbine tower collapse as a result of the coupled effects of wind and an intense, near‐field earthquake is investigated. The constitutive relation of the tower cylinder steel is simulated via a nonlinear kinematic hardening model, and the specific value of each parameter in the constitutive model is provided. A precise model of the tower structure coupled with the blade is created using a nonlinear, finite element method. This method is compared with the results from a static pushover test of a small cylindrical tower to validate the finite element modeling method in this research. Two earthquake wave sets are selected as inputs. One contains 20 near‐field velocity pulse‐like ground motion waves with various pulse periods; the other contains 20 ordinary far‐field ground motion waves. A wind turbine tower with a hub height of 60 m is selected as an example for analysis. The dynamic response of this tower as a result of the coupled effects of the two ground motion wave sets and a transient wind load is calculated using nonlinear time‐history analysis. The calculation results shows that the average horizontal displacement of the tower top as a result of the near‐field velocity pulse‐like ground motion is 33% larger than the case with far‐field ground motion. Finally, the seismic collapse vulnerability curve of this wind turbine tower is calculated. The seismic collapse capacity of the tower is evaluated, and the seismic collapse pattern of the tower is analyzed.

Cyclic loading behavior of a repaired subway station after fire exposure

After a fire, underground concrete structures, specifically in subway stations, are often repaired and reused rather than demolished. The mechanical performances of a structure after being exposed to fire require intensive evaluation before a station is reopened. This paper describes the mechanical behavior of a post-fire subway station structure by means of a structural test. A large-scale slab-column/wall structure was exposed to fire. After one of the columns damaged by fire was repaired, a combination of constant vertical load and cyclic lateral load was applied on the repaired structure. A cyclic pushover test was carried out to discover the mechanical behavior of the post-fire structure under soil pressures and service loads. Damage was accumulated as cyclic loadings increased until the structure failed due to shear crushing of the repaired column. The hysteretic loops of the entire structure were thin, indicating that fire exposure decreased the energy dissipation. Results show that the fire caused substantial damage to the structure, resulting in reduced load bearing capacity, deformation capacity, and seismic resistance.

Experimental study of double-panel confined masonry walls under lateral loading

Confined masonry structures are one of the most widely used construction systems in Algeria, in which both walls and confining elements contribute to carrying the gravity and seismic loads. Several types of confining elements are used (uniform confinements, toothed confinements), each one giving the structure a different mechanical behavior while the wall density is considered as a key safety factor for those structures. The study presented in this paper is an experimental study on two types of confinement. The study originality stems from the size of the tested samples, which included double-panel confined masonry and experimental pushover tests. First, uniform masonry walls and confinements are studied. Second, toothed masonry walls consisting of two panels of Algerian clay bricks are tested. The objectives were on one hand to study the impact of the frame/panel connection on the quasi-static behavior of the structure as well as the loading and unloading behaviors. On the other hand, to highlight the impact of using double-panel walls on resisting mechanism of confined masonry walls. Moreover, the obtained data were used for evaluating the existing analytical models to predict lateral capacities of confined masonry walls. The results indicate that the two sample-types show some similar resisting mechanisms but various capacities under progressive lateral loading, which may have consequences on the seismic resistance of the structure. A mixture of shear-flexural mechanism can be noticed when double-panel walls are used.

MONITORING OF PROGRESSIVE DAMAGE IN BUILDINGS USING LASER SCAN DATA

Abstract. Vulnerability of buildings to natural and man-induced hazards has become a main concern for our society. Ensuring their serviceability, safety and sustainability is of vital importance and the main reason for setting up monitoring systems to detect damages at an early stage. In this work, a method is presented for detecting changes from laser scan data, where no registration between different epochs is needed. To show the potential of the method, a case study of a laboratory test carried out at the Stevin laboratory of Delft University of Technology was selected. The case study was a quasi-static cyclic pushover test on a two-story high unreinforced masonry structure designed to simulate damage evolution caused by cyclic loading. During the various phases, we analysed the behaviour of the masonry walls by monitoring the deformation of each masonry unit. First a plane is fitted to the selected wall point cloud, consisting of one single terrestrial laser scan, using Principal Component Analysis (PCA). Second, the segmentation of individual elements is performed. Then deformations with respect to this plane model, for each epoch and specific element, are determined by computing their corresponding rotation and cloud-to-plane distances. The validation of the changes detected within this approach is done by comparison with traditional deformation analysis based on co-registered TLS point clouds between two or more epochs of building measurements. Initial results show that the sketched methodology is indeed able to detect changes at the mm level while avoiding 3D point cloud registration, which is a main issue in computer vision and remote sensing.

Full-scale Experimental Pushover Testing of an Existing URM Building

Due to the large number of existing unreinforced masonry (URM) buildings worldwide, and the significant seismic risk that this building stock represents, it is important to quantify the seismic behaviour of such buildings in order to provide assessment guidance to practicing structural engineers. Current assessment guidelines have received little benchmarking against the results of large scale lateral testing of typical URM buildings. In response, field testing was performed on a decommissioned vintage URM building to investigate the in-situ behaviour of URM piers and compare actual behaviour to that predicted by existing assessment frameworks. The tested building was a prototypical, three-storey, 1930s fired clay brick URM building located in Auckland, New Zealand. A pushover test was performed by applying a load to the roof level of the building with a 22 tonne excavator, resulting in the formation of a pier rocking mechanism consistent with the predicted modes determined using current assessment guidelines for URM piers. Finite element modelling was able to replicate the results of the experimental testing, but a reduction of the masonry elastic modulus when acting in tension was required in order to match experimental force-displacement response. The calibrated finite element model was subjected to a pushover analysis of the entire building and was used to benchmark the ability of common seismic assessment techniques and simplified macro-element models to predict failure mechanism and building capacity. It was found that macro-element models tended to under-predict the capacity of the building unless an artificial rigid diaphragm constraint was introduced, and that current assessment techniques and 2D macro-element modelling of individual facades provided a dependable lower bound on the capacity of URM frame-type buildings.

Enhancing the seismic performance of historic timber buildings in Asia by applying super-elastic alloy to a Chinese complex bracket system

ABSTRACTHistoric timber structures widely distributed in East Asia are suffering from the earthquakes. This article aims to develop a technique to enhance the seismic performance of historic timber buildings with the Dou-Gon system. High-strength steel bars and super-elastic alloy bars are used in this study to benchmark conventional Dou-Gon system that uses wood pegs to connect the base Dou and the column. Pushover tests were carried out under different loading conditions. The factors discussed in this study include vertical load imposed on the Dou-Gon system and the pre-strained levels of super-elastic bars. The results from this study has shown that the simple technique enhances the energy dissipation capacity and the ultimate strength of the base Dou-Gon system. Base Dou-Gon system with super-elastic alloy bar connections also show a better aseismic performance due to its constant damping behavior and longer fatigue life. Moreover, pre-strain of the super-elastic alloy bar provides a better damping behavior to the base Dou system.

A hierarchical elasto-plastic constitutive model for rammed earth

A hierarchical constitutive model based on the framework of elasto-plasticity is developed to model the mechanical behavior of rammed earth which is a quasi-brittle material. This model holds two mechanisms of plastic deformation, one related to shear failure and another one to a tensile mode of failure. Different hierarchies for the model, which are merely levels of complexity, are proposed according to the amount of information available to identify the model parameters. The model was validated simulating a diagonal compression test and a pushover test on a wallette. The simple elasto-plastic model (level-1) was able to capture some basic features of the rammed earth behaviour essentially for a rather small range of deformations, it can be used for a first estimate of the loading capacity of a system. The more sophisticated model (level-2) was able to quantitatively retrieve the non-linear behavior of rammed earth over a larger range of deformations.

Seismic performance of high-strength steel fabricated eccentrically braced frame with vertical shear link

In high-strength steel fabricated eccentrically braced frame with vertical shear link (HSSEBF-VSL), the vertical shear links use conventional steel while beam and column use high-strength steel (HSS). Using HSS for beams and columns in HSSEBF-VSL can reduce steel weight and increased economic efficiency. In this paper, static tests for two 1:2 length scaled HSSEBF-VSL specimens with one-bay and one-story were carried out, including one static pushover test and one cyclic loading test. The failure mode, load-bearing, ductility and energy dissipation capacities of the specimens were studied through the two static tests. Shake table test of a 1:2 length scaled three-story HSSEBF-VSL specimen was used to study its dynamic responses and dynamic strain responses of the vertical shear links. In addition, the finite element models of several HSSEBF-VSL and conventional EBF with vertical shear link (EBF-VSL) buildings were established for seismic effects. Nonlinear pushover and dynamic analyses were conducted to compare their seismic performance and economy. The test results indicated that the specimen with one-bay and one story had reliable lateral stiffness, ductility and energy dissipation capacity. The three-story specimen had good lateral stiffness and there was no dangerous of collapse for the specimen during the severe earthquakes. Under the same design conditions, the seismic performance of HSSEBF-VSL was slightly lower than that of EBF-VSL if it was designed to match the member section strength of EBF-VSL, but it used less steel than that of EBF-VSL, which could reduce the usage amount of steel in HSSEBF-VSL.

Experimental investigation on reparability of an infilled rocking wall frame structure

SummaryImproving seismic performance is one of the critical objectives in earthquake engineering. With the development of economy and society, reparability and fast resilience of a structure are becoming increasingly important. Reinforced concrete (RC) frame structure is prone to soft story mechanism. As a result, deformation and damage are so concentrated that reparability is severely hampered. Rocking wall provides an available approach for deformation control in RC frame by introducing a continuous component along the height. Previous researches mostly focus on seismic responses of rocking wall frame structures, while damage mode and reparability have not been investigated in detail. In this study, a novel infilled rocking wall frame (IRWF) structure is proposed. A half‐scaled IRWF model was designed according to Chinese seismic design code. The model was subjected to cyclic pushover testing up to structure drift ratio of 1/50 (amplitude 1/50), and its reparability was evaluated thereafter. Retrofit was implemented by wrapping steel plates and installing friction dampers. The retrofitted model was further loaded up to amplitude 1/30. The IRWF model showed excellent reparability and satisfactory seismic performance on deformation control, damage mode, hysteresis behavior, and beam‐to‐column joint rotation. After retrofitting, capacity of the model was improved by 11% with limited crack distribution. The model did not degrade until amplitude 1/30, due to shear failure in frame beams. The retrofit procedure was proved effective, and reparability of the IRWF model was demonstrated. Seismic resilience tends to be achieved in the proposed system.

Steel Lattice Tower Under Ultimate Load – Chosen Joint Analysis

Abstract The main objective of the presented paper is to discuss chosen lattice tower joint behavior under structure ultimate load. Joint numerical modelling considerations are enriched with comparison to the full-scale tower pushover test results. Two independent load cases were examined: 1) where the L-sections (diagonal bracings) are loaded by the axial force only and that forces are applied in the center of the member cross section, 2) where the L-sections are loaded by the axial force and the bending moment that reproduce the effect of the eccentric connection to the gusset plates by the one leg of the angle section is added. Differences in equivalent stresses state for two independent design situations allow for conclusion that additional bending moments should be taken into account, especially for thin-walled members.

Applied element method simulation of experimental failure modes in RC shear walls

With the continuous evolution of the numerical methods and the availability of advanced constitutive models, it became a common practice to use complex physical and geometrical nonlinear numerical analyses to estimate the structural behavior of reinforced concrete elements. Such simulations may yield the complete time history of the structural behavior, from the first moment the load is applied until the total collapse of the structure. However, the evolution of the cracking pattern in geometrical discontinuous zones of reinforced concrete elements and the associated failure modes are relatively complex phenomena and their numerical simulation is considerably challenging. The objective of the present paper is to assess the applicability of the Applied Element Method in simulating the development of distinct failure modes in reinforced concrete walls subjected to monotonic loading obtained in experimental tests. A pushover test was simulated numerically on three distinct RC shear walls, all presenting an opening that guarantee a geometrical discontinuity zone and, consequently, a relatively complex cracking pattern. The presence of different reinforcement solutions in each wall enables the assessment of the reliability of the computational model for distinct failure modes. Comparison with available experimental tests allows concluding on the advantages and the limitations of the Applied Element Method when used to estimate the behavior of reinforced concrete elements subjected to monotonic loading.

A STUDY ON THE PUSHOVER TEST AND NUMERICAL ANALYSIS OF GFRP FRAMES

This paper presents the use of glass fiber reinforced plastic (GFRP) composite material to produce a structure frame; the behaviors of the GFRP frames were analyzed by using pushover test and a numerical analysis software. Double-web FRP I-beams are used for the beams and columns of the frame, and joints made from metal and FRP. Three types of frame specimens were involved: an un-braced frame, a compression-braced frame and a tension-braced frame for each joint type. The joints were bonded to the frame components using epoxy resin but also adding bolts in the beam-column joint. The pushover test was used to investigate the mechanical behaviors and failure modes of the GFRP frames. The analysis software SAP2000 was used for the pushover analysis of the GFRP frames, and it was shown that the ultimate strength and force-displacement relationships of the analytical results were similar to that of the experimental ones.

Experimental assessment of the seismic behavior of unbraced steel storage pallet racks

Steel storage racks are typically made of thin-walled cold formed steel profiles, which prove to be the most versatile, economic and sustainable elements for industrial rack construction. Their lightweight structural systems are usually designed to resist heavy load units, reaching considerable heights. However, the global behavior of storage racks under seismic actions is much less predictable than the behavior of steel buildings made of standard steel profiles and connections, mainly due to the perforations in their thin walled upright columns, and their semi-rigid beam-column and base plate joints. Full scale experimental investigations are greatly needed in order to understand and quantify the global performance of storage racks, and improve their design for seismic actions.For the first time in Europe, thanks to the funding provided by Research Fund for Coal and Steel (RFCS), an extensive full-scale push-over testing program has been carried out on 8 fully-loaded pallet racking specimens (4 unbraced and 4 braced racks), provided by 4 different international rack producers.This paper presents the experimental results of full scale push-over tests performed in the down-aisle (longitudinal) direction on fully-loaded unbraced specimens. In particular, experimental global capacity curves of the tested specimens are presented, discussing the key factors influencing the racks’ response, as well as the failure mechanisms of the different rack typologies. Furthermore, the behavior factor (q) values of each specimen are derived from re-analysis of the test results. Vulnerability of unbraced racks to soft-storey mechanism is demonstrated, highlighting its causes. Design guidelines are provided in order to guarantee a globally homogenous ductility under seismic actions, along with the new safety requirements for the design of the floor connections of unbraced racks.