Quasi-static Cyclic Tests Research Articles

Experimental and numerical study on seismic behavior of obliquely stiffened steel plate shear walls with openings

Abstract To study the influence of frame-to-plate connections and oblique channel-shaped stiffeners on the seismic behavior of steel plate shear walls (SPSWs), cyclic quasi-static tests were carried out on two one-bay two-story specimens. One specimen was diagonally stiffened with two rectangular openings, and the other was multi-obliquely stiffened with one rectangular opening. The bearing capacity, ductility, degradation characteristics, and energy dissipation of two specimens were analyzed. Furthermore, following the test program, the stress distribution, deformation and fracture tendency of the two specimens were simulated by the finite element (FE) software ABAQUS and validated by the experimental results. The experimental results show that the channel-shaped stiffeners make full use of the larger flexural and torsional stiffness and improve the bearing capacity, stiffness, and elastic buckling load of the structures. Moreover, the oblique stiffeners have an obvious bracing effect, so the web of the middle beam is subjected to shear yield at the opening segment, which is similar to the link in the eccentrically braced frame. The inelastic mechanism is transferred from the steel plate to the link. In the plastic stage of the structure, the stiffened plate is basically elastic, and the seismic energy is mainly consumed by the link. Therefore, this kind of steel plate shear wall needs to consider the additional effect of the stiffeners on the boundary elements. The reasonable design of the link segment enables the frame to have enough strength to support the stiffened plate as well as avoid premature yielding at the link.

Design, simulation and test on the shape optimization of a steel shear key (SSK)

Prefabricated reinforced concrete shear walls are widely used because of their stiffness, strength and convenient form of construction, despite their low ductility and energy dissipation capacity. For ease of transport, large shear walls are commonly divided into smaller sections and assembled on site. Steel shear keys (SSKs) can replace wet joints connecting the wall sections while increasing the ductility and energy dissipation of shear wall systems. Here, we present an improved SSK design and a practical installation method for connecting shear walls. The SSK shape is optimized through an Improved Simulated Annealing method to enhance the cycle fatigue performance. Fillet welding and plug welding are combined to save the installation space and delay the out-of-plane buckling. Quasi-static cyclic tests were performed to investigate the SSKs with the welded connection, which exhibited satisfactory energy dissipation capacity. The combined welding method provided a strong SSK–wall connection while significantly delaying out-of-plane buckling.

Investigation on seismic behavior of bridge piers with thin-walled rectangular hollow section using quasi-static cyclic tests

This study aims to investigate the seismic behavior of thin-walled rectangular hollow reinforced concrete (RC) bridge piers through quasi-static cyclic tests. For this purpose, two identical 1:12 scale specimens were designed and tested under different loading protocols. One specimen was subjected to displacement-controlled cyclic lateral loading with a constant axial load, and the other to the same lateral loading history, but with a variable axial load. The behavior of both specimens was evaluated in terms of the damage progression and failure mode, concrete crack width, hysteretic response, backbone curve, and residual displacement. The results revealed that both specimens experienced a mixed flexure-shear damage progression from the first crack through collapse. Flexural cracks were first observed in the flange surfaces, followed by the development of shear diagonal cracks in both web surfaces. Meanwhile, both specimens exhibited stable hysteretic behavior. Then, concrete spalling and longitudinal bar buckling were concentrated at the corners of the flanges due to the shear lag effect. Eventually, both specimens collapsed as a result of the flange local compression buckling. In addition, the specimen under a variable axial load collapsed much severer than the one under a constant axial load. Ultimate drifts of the specimens under a constant or variable axial load were 2.25% and 2%, respectively. This experiment provides valuable dataset for validating advanced numerical modeling techniques for thin-walled rectangular hollow RC piers, especially the data points in the collapse stage.

Quasi-static cyclic tests of confined masonry walls retrofitted with mortar overlays reinforced with either welded-wire mesh or steel fibers

Overlays made of high-slump mortar reinforced with a steel welded-wire mesh are one of the most common techniques to retrofit low-rise confined masonry walls. An alternative to this technique is the use of Steel Fiber-Reinforced Mortar (SFRM) overlays to strengthen and enhance the shear capacity of existing masonry walls. In this paper, test results are presented of two full-scale, multi-hollow clay brick confined walls strengthened with reinforced mortar overlays. The overlays consisted of a high-slump mortar reinforced with a) welded-wire reinforcement in one wall and b) hooked end steel fibers in the second wall. Overall height and length of the walls were 2.5 m and 4.24 m, respectively. Both walls were tested under in-plane, quasi-static, reversed cyclic lateral loads. Performance of the retrofitted walls is evaluated in terms of crack patterns, hysteretic response, and lateral strength and displacement capacity. The test data show that both retrofit techniques performed very well and they each restored the strength and deformation capacity to that of the original walls.

Experimental and numerical study on coupled shear walls with buckling-restrained steel plates under cyclic loading

This paper aims to investigate the seismic behavior of coupled shear wall with buckling restrained steel plates (CW-BRSP) under cyclic lateral loading. The quasi-static cyclic test on a 1/3-scaled CW-BRSP specimen was conducted. The response of CW-BRSP under cyclic loads, including the damage and failure modes, lateral force-displacement relationship, strength and stiffness degradation, energy dissipation, were observed as well as compared with those of the solid and coupled concrete shear walls. Yielding and plasticity of the buckling restrained steel plates developed with the increment of loading amplitude. Flexural cracks developed at the base of the wall piers. Test results indicated that the proposed CW-BRSP system has stable lateral load resisting and energy dissipation capacity. In addition, refined nonlinear finite element model of the CW-BRSP was developed and validated. Parametric study results indicated that the axial load ratio, degree of coupling and strength of buckling restrained steel plates has significant effect on seismic behavior of the CW-BRSP.

Seismic Performance of Precast Bridge Columns with Socket and Pocket Connections Based on Quasi-Static Cyclic Tests: Experimental and Numerical Study

AbstractIn this study, four 1/3-scale bridge column specimens were investigated both experimentally and numerically. The specimens consisted of two cast-in-place (CIP) reference columns and two pre...

Seismic fragility analysis of concrete encased frame‐reinforced concrete core tube hybrid structure based on quasi‐static cyclic test

SummaryConcrete‐encased frame‐core tube hybrid structural system has been widely employed in high‐rise buildings. This paper intends to analyze the seismic fragility of this structural system under ground motion excitation. The quasistatic cyclic test on a 1/5‐scaled, 10‐story three‐bay specimen is introduced. Fiber‐based finite element model is developed and integrated with numerical techniques that would be able to simulate the nonlinear response based on the OpenSees program. As the model is verified by the experimental data, a series of incremental dynamic analyses (IDAs) considering different frame‐tube stiffness ratios are carried out. IDA curves are drawn to describe each structural performance state. Fragility curves and probabilistic demand models are proposed for quantifying failure probability. The collapse margin ratio is employed to evaluate the collapse probability. The result shows that the collapse probability under rare earthquake still meets the requirement of Applied Technology Committee‐63 Report. The hybrid structure is proved to perform superior collapse resistance ability. The proper increase in the stiffness of core tube can reduce the collapse probability and enhance the collapse resistance capacity.

Photogrammetric Solution for Analysis of Out-Of-Plane Movements of a Masonry Structure in a Large-Scale Laboratory Experiment

This paper proposes a photogrammetric procedure able to determine out-of-plane movements experienced by a masonry structure subjected to a quasi-static cyclic test. The method tracks the movement of circular targets by means of a coarse-to-fine strategy. These targets were captured by means of a photogrammetric network, made up of four cameras optimized following the precepts of a zero-, first-, and second-order design. The centroid of each circular target was accurately detected for each image using the Hough transform, a sub-pixel edge detector based on the partial area effect, and a non-linear square optimization strategy. The three-dimensional (3D) coordinates of these targets were then computed through a photogrammetric bundle adjustment considering a self-calibration model of the camera. To validate the photogrammetric method, measurements were carried out in parallel to an ongoing test on a full-scale two-story unreinforced masonry structure (5.4 × 5.2 × 5.4-m) monitored with more than 200 contact sensors. The results provided by the contact sensors during one of the load phases were compared with those obtained by the proposed approach. According to this accuracy assessment, the method was able to determine the out-of-plane displacement during the quasi-static cyclic test with a sub-pixel accuracy of 0.58.

Retrofitting external RC beam-column joints of an ordinary MRF through plastic hinge relocation using FRP laminates

This paper presents the results of experimental and numerical investigations on flange and web -bonded FRP retrofitting schemes for external RC joints of moment resisting frames. Two, identical full-scale external joints are designed and constructed according to ACI318M-11 requirements for ordinary moment resisting frames. Quasi-static cyclic loading tests are then carried out on the specimens and some seismic performance parameters including strength, ductility, energy dissipation and stiffness are evaluated and compared. Numerical analyses are also carried out to study the effects of FRP overlay length on required number of plies for plastic hinge relocation and joint strength. It is found that successful relocation of plastic hinge away from the face of the column into the beam is possible with appropriate number of FRP laminate plies and overlay length. It is also found that as the length of the FRP laminate over the beam flange increases, the joint strength is enhanced; however, larger number of plies would be required for plastic hinge relocation.

Behaviour of wall segments and floor slabs in precast reinforced concrete shear walls assembled using steel shear keys (SSKW)

Reinforced concrete (RC) precast shear walls are commonly used in building structures. For transportation ease, large walls are divided into smaller segments and assembled at the construction site with various connection methods. This study focussed on the RC precast shear wall assembled using steel shear keys, which is simply called the steel shear key wall (SSKW) in this paper. Three SSKW specimens were designed and built by considering different sizes and numbers of shear keys. Quasi-static cyclic loading tests were performed to investigate the strength and stiffness of the assembled SSKWs and the behaviour of the wall segments and floor slab. We found that adding strength and more shear keys gradually increased the lateral resistance and stiffness of the specimens and decreased the distortion and damage to the floor slabs. However, the specimens also exhibited lower ductility and energy dissipation with increasing link strength. Finally, an appropriate coupling ratio for SSKWs was suggested for their design in practical engineering.

Influence of shear span ratio on the seismic performance of L-shaped RC walls

Owing to their capability of meeting both structural and architectural demands, L-shaped reinforced-concrete (RC) walls are widely employed in low-rise and high-rise buildings. In spite of their popularity, the experimental data on the seismic performance of these walls is relatively sparse, especially with respect to their behaviour under lateral loads that are not parallel to the wall segments. In order to obtain improved understanding of such walls, quasi-static cyclic tests on six slender L-shaped RC walls were conducted under displacement control in Nanyang Technological University (Singapore). Through comparison with four squat L-shaped RC walls described in the literature, the influence of shear span ratio was highlighted in terms of cracking patterns, failure mechanisms, hysteretic responses, deformation components and strain profiles. Moreover, shear lag effect and effective stiffness were analysed using non-linear section analyses and methods available in the literature. The results showed the shear span ratio had a significant impact on the seismic performance of L-shaped RC walls, and should be addressed discretely in the design.

Effect of transverse reinforcement on the seismic behavior of diagonally reinforced concrete coupling beams

Coupled shear wall systems have been more popularly used in high-rise building construction in urban areas due to their efficiency in sustaining lateral loads as well as economic effectiveness. During earthquakes, coupling beams in the coupled wall system act as a seismic fuse element that dissipate most of seismic input energy exerted in the system. Diagonally reinforced concrete coupling beams (DRCBs) have been developed for this purpose. The objective of this study was to acquire test data of DRCBs of with different amount of transverse reinforcement and to evaluate the seismic behavior of these DRCBs. Quasi-static cyclic tests were conducted using seven DRCB specimens with different amounts of transverse reinforcement and different aspect ratios. Four specimens had Ln/h of 2.0, whereas it was 3.5 for the other three specimens. The shear strengths of individual specimens were compared to that calculated from the shear strength equation specified in ACI 318-14, and their deformation capacities were compared to those specified in ASCE 41-17. It is observed that the amount of transverse reinforcement in DRCBs played an important role in their shear strength and deformation capacities, indicating that the contribution of transverse reinforcement needs to be incorporated to ACI 318 shear strength equation and ASCE 41-17 model parameters.

Experimental determination and numerical simulation of material and damage behaviour of 3D printed polyamide 12 under quasi-static loading

In order to characterise the material and damage behaviour of additively manufactured polyamide 12 (PA12) under quasi-static load and to implement it in a numerical model, experiments under quasi-static load as well as microstructural investigations were carried out. Selective laser sintering (SLS) was used as the manufacturing process. For the classification of the material behaviour, quasi-static cyclic tests with holding times as well as tensile tests were performed. X-ray refraction and computed tomography (CT) were used to investigate the damage behaviour. The Chaboche model, which has already been applied for metallic materials under thermomechanical loading, served as the basis for the selection of the numerical material model. The same procedure was used for the selection of the damage model, where the Gurson–Tvergaard–Needleman (GTN) model was chosen, which was already used for porous metallic materials. The Chaboche model shows very good agreement with experimental results. Furthermore, the coupling with the GTN model allows a very good modelling of the damage behaviour. Finally, it could be shown that the selected models are suitable to simulate the material and damage behaviour of 3D printed PA12.

A practical approach to predict the hysteresis loop of reinforced concrete columns failing in different modes

Accurate prediction of hysteresis loop of reinforced concrete (RC) columns in different failure modes is of utmost importance for the assessment of inelastic seismic performance of structures. In this paper, a practical approach is proposed by adopting the Bouc-Wen-Baber-Noori (BWBN) model to describe the typical hysteresis characteristics of RC columns, and applying the Artificial Neural Network (ANN) model to evaluate the BWBN model parameters. The governing equation of the BWBN model is first presented in terms of inelastic restoring force-translational displacement relationship according to the experimental data of RC columns under quasi-static cyclic testing. The structural performance database compiled by Pacific Earthquake Engineering Research (PEER) center is then adopted to determine the BWBN model parameters using the differential evolution (DE) algorithm. Furthermore, the ANN model is implemented to associate the identified BWBN model parameters with dimensionless physical parameters of RC columns failing in different modes. According to the investigation, it is found that the magnitude of BWBN model parameters is considerably affected by specific failure mode of RC columns. The accuracy of the estimated BWBN model parameters using the ANN model is examined, in which the hysteresis loop of RC columns failing in different modes can be reasonably quantified by the proposed approach.

Experimental study on seismic performance of RC frames with Energy-Dissipative Rocking Column system

The conventional reinforced concrete Moment Resisting Frames (MRFs) have suffered from soft story failure during major earthquake events. A novel system of steel Energy-Dissipative Rocking Column (EDRC) is proposed to mitigate seismic responses of MRFs. Pseudo-dynamic tests are conducted on large-scale two-story and two-bay reinforced concrete frames, with and without EDRC, respectively. The post-earthquake behavior of these two systems is also compared through quasi-static cyclic tests. The experimental results show that the presence of EDRC can effectively mitigate the maximum value, residual value and inhomogeneous distribution of inter-story drifts, and thus prevent the soft story failure of MRFs. It is found that the maximum and residual inter-story drift of combined MRF and EDRC systems is reduced by 26.0% and 82.0%, respectively, compared to pure MRFs. The inhomogeneous degree of inter-story drifts can be reduced by 25.0% and 11.0%, respectively, in the pseudo-dynamic and quasi-static tests.

Seismic demand and capacity assessment of suspended ceiling systems

In recent years, scientific interest for the study of Non-Structural Elements (NSE) has significantly increased and the importance of the seismic safety of these elements has become a widely discussed topic. Several technologies able to guarantee the seismic safety of NSE were created. In particular the sector of suspended ceiling has seen the development of different systems for achieving this purpose. Specific internal joints between profiles, perimeter brackets and bracing systems have been created to realize “anti-seismic” suspended ceilings. Several shake table tests, also defined qualifying tests, have been performed to analyze the behaviour of these systems.This work presents new original studies on seismic behaviour of suspended ceilings with an experimental fragility approach. Recently cyclic quasi-static tests have been realized at the University of Padova by means of a specifically developed experimental setup. First, experimental results were processed to define the hysteretic capacity curves of a typical metal T-Grid suspended ceiling. Then, these curves were exploited by means of numerical analyses to determine the elastic and inelastic response of the suspended ceiling installed at various levels of five multi-storey frames characterized by different vibration periods. Linear dynamic analyses of the frames subjected to 7 spectra-compatible artificial seismic signals were performed to obtain floor acceleration signals and spectra. Then three alternative numerical approaches were employed to define the seismic demand on the suspended ceiling. Using a displacement-based approach, capacity curves and elastic floor spectra were compared in the ADRS (Acceleration Displacement Response Spectrum) domain to evaluate the elastic displacements and accelerations of the suspended ceiling (Spectral Analysis). Also, Linear and Non-Linear Time-History analyses of the NSE were performed according to a cascade approach. The comparison of the seismic demands resulting from elastic, inelastic and spectral analyses is reported in the paper for each of the frames.

Damage effect on experimental modal parameters of haunch strengthened concrete-encased composite column–beam connections

This paper presents an experimental study about the effects of damage on modal parameters of haunch strengthened composite column–steel beam connections. Five specimens having various composite column and steel beam connection details were constructed in order to be examined in laboratory condition. Non-destructive experimental measurements were conducted to extract the modal parameters using frequency and time domain methods before and after damage conditions. Quasi-static cyclic tests were performed to assess the damaged conditions in connection zones of the test specimens. At the end of the study, it is observed distinctly that there is a decreasing trend in natural frequencies with damages. Also, no compliance is observed between mode shapes pre- and post-cycling loading tests. The biggest dissimilarities concerning natural frequencies were determined among 26.57% and 36.54%. The value for modal assurance criterion was 1.0 for undamaged condition. However, in post-damaged situation, the mode shapes have changed and modal assurance criterion values nearly approached zero. Finally, experimentally obtained damping ratios have been analyzed. The outcome of the study has shown some dissimilarity and that the values are not being correlated constructively. Despite the fact that the results are consistent with the available literature, it is assumed that these dissimilarities point to the fact that higher levels of excitation might be need to precisely record the damping ratios.

A Simplified Approach to Investigate the Seismic Ductility Demand of Shear-Critical Reinforced Concrete Columns Based on Experimental Calibration

ABSTRACT A simplified approach is proposed to investigate the seismic ductility demand of shear-critical reinforced concrete (RC) columns based on experimental calibration. Incorporating with the Bouc–Wen–Baber–Noori (BWBN) model, the governing equation of the equivalent single-degree-of-freedom (SDOF) system is first presented to describe the typical hysteresis characteristics, where the relationship between the inelastic restoring force and translational displacement is calibrated by comparing with the experimental data of shear-critical RC columns under quasi-static cyclic testing. Based on the developed governing equation, the strength reduction approach is further implemented to estimate the seismic ductility demand of shear-critical RC columns by establishing the constant strength-ductility demand spectral (CSDDS) method. Finally, an empirical expression is regressed to predict the mean and standard deviation of seismic ductility demand of shear-critical RC columns. This study verifies the feasibility of the proposed approach to assess the seismic ductility demand of shear-critical RC columns. The presented idealized SDOF system can simplify the establishment of CSDDS method. The lognormal assumption cannot well describe the probabilistic characteristics of seismic ductility demand if all the uncertainties in model parameters and earthquakes are considered. The developed empirical expression is applicable to investigate the probabilistic seismic risk of shear-critical RC columns under different earthquake excitations.

Seismic design of the double-cell accordion-web reduced beam section connection

The Accordion-Web Reduced Beam Section (AW-RBS) connection consists of a corrugated web, replacing the flat web, within a limited area near the column face, which reduces the beam flexural strength and forces the plastic hinge to form in the corrugated zone. This paper presents a seismic design procedure in the framework of the U.S. design standards for a double-cell AW-RBS connection, which consists of two box sections oriented such that an accordion web is formed within a limited area in the beam. The analytical evaluation of the flexural strength of the beam with a corrugated web was first presented. Then, a step-by-step design method was proposed to size the connection. Quasi-static cyclic tests were conducted on two relatively identical specimens including double-cell AW-RBS connections. A detailed numerical model of a connection with deep beams and columns designed in accordance with the proposed design procedure was developed and a nonlinear analysis was performed to investigate the seismic response of the connection and verify the adequacy of the proposed design method for the beam sizes frequently used in steel moment-resisting frames. The results confirmed the satisfactory response of the double-cell AW-RBS connection under cyclic loading. The stable plastic hinge formed in the reduced area of beams as predicted in design and no yielding was observed in the beam-to-column groove weld. The findings of the numerical simulations confirmed that the AW-RBS connection with deep beams and columns could potentially exceed the plastic rotation limit for ductile moment connections without significant instability and strength degradation.

Predictive equations for drift ratio and damage assessment of RC shear walls using surface crack patterns

The purpose of this paper is to quantify the extent of damage of rectangular reinforced concrete shear walls after an earthquake using surface crack patterns. One of the most important tasks after an earthquake is to assess the safety and classify the performance level of buildings. This assessment is usually performed by visual inspection that is prone to significant errors. In this research, an extensive database on the images of damaged rectangular reinforced concrete shear walls is collected from the literature. This database includes more than 200 images from experimental quasi-static cyclic tests. Using the concept of fractal geometry, several probabilistic models are developed by extracting and regenerating the surface crack patterns of the collected walls. These models can estimate the peak drift ratio that the structure has experienced. The peak drift ratio predicted by the proposed models of this paper can be used to calculate the probability of exceedance of different damage states using existing fragility models. Furthermore, new fragility models are directly developed using the images of the damaged walls of the collected database. The proposed fragility curves calculate the probability of exceedance of damage states using the crack pattern of the damaged shear walls and consequently provide an estimation of the loss, repair cost, and repair time of the walls.