Experimental Cyclic Behavior Research Articles

Experimental cyclic behavior of concrete interfaces with postinstalled reinforcing bars or alternative connectors

AbstractIn this experimental campaign, concrete‐to‐concrete interfaces were examined under cyclic actions, crossed by postinstalled reinforcing bars or industrial steel screws. In addition, the effect of the embedment length and the roughness was investigated. It was observed that different failure modes occur, depending on the different connector types and embedment depths. The positive effect of roughness on the interface resistance was confirmed, but the results indicate that, for very high roughness values, the resistance may be smaller than for moderate values. It was also noticed that the behavior of interfaces crossed by mechanical anchors was less stiff in the ascending branch and exhibited a less steep falling branch. The extension of the project on testing thin overlays showed that the resistance was significantly affected in case of cyclic loading, suggesting that the use of any type of anchor in seismic conditions needs to be supported by adequate experimental evidence.

Modeling and Verification of Multi-Strut Modeling Approach of Masonry Panel Surrounded by RC Frame

Bangladesh which lies in an earthquake-prone region, possesses many seismically vulnerable structures and would need to be strengthened for future usage following the current building code. In this context, assessing the responses of the existing building frames with or without infilled masonry is essential for designing an adequate strengthening scheme that would be suitable for the building. The current study intends to model and simulate one of the available masonry infilled test specimens where the fiber modeling approach of RC member and the multi-strut model of infill masonry have been considered. In addition, the numerically obtained lateral strength has also been compared with analytically evaluated lateral strength. The lateral responses obtained from the numerical analysis showed a fair agreement with the experimental cyclic behavior having a ratio of experimental to the numerical lateral capacity of 0.97. The numerical lateral strength also indicates good conformity with analytical evaluation having an analytical to numerical lateral capacity ratio of 1.13. Journal of Engineering Science 13(2), 2022, 21-29

Settlement of Ring Footing Resting on Geocell Reinforced Sandy Soil under Cyclic Load

Ring footings are widely used as a foundation for water tanks, television antennas, silos, chimneys, oil storage tanks, etc. This paper is conducted to study the ring footing model's experimental cyclic behavior and circular footing resting on sandy soil reinforced with geocell. A group of ninety-six test models has been tested to investigate shallow footings' behavior beneath a cyclic loading of various loading rates. Four shapes of footing sand with three relative densities, two embedment depths of footing, two loading rates, and two widths of geocell were used. It was founded that as the footing depth increases, the settlement of soil due to cyclic loading decreases. Generally, when other variables are maintained to be the same, the footing bearing capacity increases when the foundation depth increases. The footing rebounds to some degree during the decay period of the load. The presence of geocell at the footing depth equals 100 mm will provide more improvement in all footing models more than using it at the surface, especially in ring 2 where the radius ratio is 0.4.

Experimental cyclic behavior of code-conforming exterior wide beam-column connections

Reinforced concrete (RC) frames with wide beams are efficient systems for resisting against lateral and gravity loads. However, there are limited experimental studies on the performance of wide beams under cyclic lateral loading. This paper presents the results of an experimental investigation on seismic behavior of RC exterior wide beam-column connections. Four 3:5 scale wide beam-column connections were tested under combined constant axial and quasi-static cyclic lateral loads. Different spandrel beam types including conventional and wide beam and three column geometries (square, rectangular and circular) were used in the specimens. The specimens all were designed in accordance with ACI 318-14 and ACI 352R-02 provisions. Special attention was given to reinforcement detailing of wide beam and spandrel beam at the joint area. The test results showed that although all specimens were code conforming and similarly designed for interaction of bending, shear and torsion, more torsional cracks developed in the cases that transverse beam was wide. The performance of all the specimens was satisfactory in terms of strength, ductility and energy dissipation capacity. It was observed that the load transfer mechanism from wide spandrel beam to column is a combination of torsion and bending. In the specimen with circular column, higher displacement ductility and lower energy dissipation were observed compared with the similar specimen containing square column. Besides, the importance of fine reinforcement detailing for wide and spandrel beam at the joint zone was confirmed by the test results.

A corrosion model for the interpretation of cyclic behavior of reinforced concrete sections

AbstractA generalized cyclic steel model characterized by isotropic and kinematic hardening, inelastic buckling in compression and corrosion of rebars in reinforced concrete (RC) structures is presented. The model has been implemented in a fiber code, to perform seismic analyses of RC sections. The model is particularly accurate with respect to experimental cyclic behavior of rebars with buckling in compression when the strain does not exceed 1.5%. Twelve configurations of RC cross sections were selected as case studies for three geometries and different steel arrangements, assumed representative of RC columns or bridge piers (in a suitable scale). Each section was subjected to two groups of cyclic curvature histories representative of severe seismic loads, not far from collapse. Different axial loads and corrosion percentages (no corrosion, moderate, or high) have been selected to perform cyclic parametric analyses. One of the cases was taken from an experimental test on columns, deriving also steel characteristics used in all numerical cases. The results of the comparison among RC sections have been discussed. Numerical results show that the maximum compressive strain for steel rebars is always smaller than 1.5%, therefore the proposed steel model is accurate and represents a valid tool for structural assessment. Corrosion reduces RC section capacity, affecting various rebar mechanical characteristics, in particular buckling behavior.

Experimental cyclic behavior of connection to double-skin composite wall with truss connector

Double-skin composite walls have been increasingly applied in high-rise buildings. The behavior of connection to the wall under seismic action is essential to the performance of the whole structures. This paper investigated the experimental seismic behavior of four proposed connections to an innovative double-skin composite wall. The wall employs steel trusses as internal connectors. Large-scaled cyclic tests were performed on connections with different configurations. The seismic behavior was evaluated in terms of failure mode, hysteretic response, stiffness degradation, ductility, and energy dissipation ability. The test results found that all specimens exhibited stable and plentiful hysteretic performance without noticeable pinching effect. Reasonable stiffness degradation, good ductility and satisfying energy absorbing capacity were also observed. Strain distributions at key locations were analyzed to evaluate the strain development at beam, stiffener, and wall face. It is concluded that the connection with vertical stiffeners has good seismic behavior. The application of vertical plate or additional cover plate is also acceptable. In addition, the use of through plate should be careful as the welding quality is important to the behavior of connections.

Experimental cyclic behavior and constitutive modeling of high strength structural steels

High strength structural steels have recently achieved increasing application in civil and structural engineering worldwide. For instance, the sony center tower located in Berlin were constructed through steel truss made of S460 and S690 high strength steel whose nominal yield stress is 460 MPa and 690 MPa respectively. The utilization of high strength steel considerably reduced the structure deadweight and produced larger architecture space. Besides, steel connections of one military steel bridge in Mittådalenthe, Sweden were fabricated of 960 MPa ultra-high strength steel. This application remarkably increases the construction convenience since high strength steel presents excellent ability to reduce member size as well as improve structure performance. Nevertheless, limited test data have been available on the monotonic properties and cyclic behavior of these structural steels. In this study, uniaxial coupons were tested for four types of Chinese high strength structural steels, including grades Q460D, Q550D, Q690D as well as ultra-high strength structural steel Q890D, to investigate their stress-strain response and energy-dissipation behavior under monotonic and various cyclic strain demands. The monotonic test results of the tested steels were then compared with the requirements of current seismic design codes GB 50011-2010 and Eurocode8. Besides, cyclic strength, deformability and energy dissipation capacity were evaluated through the tested strain-stress loops. The experimental observations in cyclic tests show that cyclic softening, which significantly affects the shape of cyclic loops and energy dissipation capacity, is an important hysteretic characteristic for all tested high strength structural steels. Moreover, cyclic backbones of these four steels were calibrated using Ramberg-Osgood model. To fundamentally define the cyclic stress-strain relationship, essential parameters of three commonly used constitutive models, including Chaboche model, Dong-Shen model and Giuffre-Menegotto-Pinto model were calibrated based on the experimental data under cyclic loading. Those calibrated models were then employed in simulations of aforementioned cyclic loading tests and their validity were compared. Good agreements between experimental response and simulated performance by Dong-Shen model were achieved, demonstrating that the calibrated Dong-Shen model can elaborately describe the cyclic behavior of these four types of high strength structural steels.

Experimental Cyclic Behavior of Precast Hybrid Beam-Column Connections with Welded Components

Post-earthquake observations revealed that seismic performance of beam-column connections in precast concrete structures affect the overall response extensively. Seismic design of precast reinforced concrete structures requires improved beam-column connections to transfer reversed load effects between structural elements. In Turkey, hybrid beam-column connections with welded components have been applied extensively in precast concrete industry for decades. Beam bottom longitudinal rebars are welded to beam end plates while top longitudinal rebars are placed to designated gaps in joint panels before casting of topping concrete in this type of connections. The paper presents the major findings of an experimental test programme including one monolithic and five precast hybrid half scale specimens representing interior beam-column connections of a moment frame of high ductility level. The required welding area between beam bottom longitudinal rebars and beam-end plates were calculated based on welding coefficients considered as a test parameter. It is observed that the maximum strain developed in the beam bottom flexural reinforcement plays an important role in the overall behavior of the connections. Two additional specimens which include unbonded lengths on the longitudinal rebars to reduce that strain demands were also tested. Strength, stiffness and energy dissipation characteristics of test specimens were investigated with respect to test variables. Seismic performances of test specimens were evaluated by obtaining damage indices.

Experimental cyclic behavior and constitutive modeling of low yield point steels

To fundamentally define the cyclic behavior of low yield point steel (LYP) and obtain representative material constitutive parameters for structural analysis, experimental studies of LYP100 and LYP160 steels were conducted under a range of loading scenarios. Monotonic and cyclic loading patterns were used to evaluate overall response characteristics and to quantify strength, ductility and energy dissipation capacity. Based on this experimental data, the essential material parameters of two constitutive models were calibrated. These constitutive models were then employed in structural analysis of previous large-scale steel plate shear wall test specimens, and the analysis results agreed well with the test data. Together, the experiments and analyses conducted in this study indicate that, although the yield strengths of LYP steels are by design less than conventional and high strength steels, characteristics that are important for seismic behavior – such as cyclic response, ductility and energy dissipation capacity – are improved. Cyclic response of LYP steel is characterized by combined isotropic and kinematic hardening, and the isotropic component plays a more significant role. LYP steel is a promising structural material that can be employed more effectively when its cyclic behavior, including appreciable hardening, is defined through experimental studies and constitutive modeling as presented here.

A regularized fiber element model for reinforced concrete shear walls

SummaryReinforced concrete shear walls are used because they provide high lateral stiffness and resistance to extreme seismic loads. However, with the increase in building height, these walls have become slenderer and hence responsible of carrying larger axial and shear loads. Because 2D/3D finite element inelastic models for walls are still complex and computationally demanding, simplified but accurate and efficient fiber element models are necessary to quickly assess the expected seismic performance of these buildings. A classic fiber element model is modified herein to produce objective results under particular loading conditions of the walls, that is, high axial loads, low axial loads, and nearly constant bending moment. To make it more widely applicable, a shear model based on the modified compression field theory was added to this fiber element. Consequently, this paper shows the formulation of the proposed element and its validation with different experimental results of cyclic tests reported in the literature. It was found that in order to get objective responses in the element, the regularization techniques based on fracture energy had to be modified, and nonlinearities because of buckling and fracture of steel bars, concrete crushing, and strain penetration effects were needed to replicate the experimental cyclic behavior. Thus, even under the assumption of plane sections, which makes the element simple and computationally efficient, the proposed element was able to reproduce the experimental data, and therefore, it can be used to estimate the seismic performance of walls in reinforced concrete buildings. Copyright © 2016 John Wiley & Sons, Ltd.

Seismic Behavior of Masonry Walls: Modeling of Hysteretic Rules

A method of modifying the lateral load–lateral displacement relationship obtained by a simple monotonic racking test to represent the skeleton hysteresis curve of an arbitrary dynamic response of a reinforced-masonry wall is proposed. The results of tests of 32 equal reinforced-masonry walls, tested by imposing monotonically increasing displacements, cyclic lateral displacements of two different shapes, and simulated displacement seismic response, have been used as a basis for the development of the procedure of modification. The amount of input energy, defined as the actuator work done to deform the specimens during the test, has been taken into account as the decisive parameter for carrying out this modification. On the basis of experimental results, correlation factors between the monotonic and cyclic hysteresis envelope curves, as well as stiffness and strength degradation parameters, which define the hysteretic rules, have been evaluated. Good agreement between predicted and experimental cyclic behavior of the walls has been obtained.

Cyclic Behavior of Structural Steels. II: Theory

This paper is concerned with the analytical modeling of the cyclic behavior of structural steels. The modified uniaxial two-surface model developed by Shen et al. in 1992 is generalized to a multiaxial two-surface model, which can treat the cyclic behavior of the structural steels even within the yield plateau. The important features of the cyclic behavior observed in the uniaxial and biaxial cyclic experiments are included in the present model with the extension of the effective plastic strain (EPS) range concept into the multidimensional stress state. The experimental cyclic behavior of mild steel under nonproportional biaxial (torsion-compression) loading histories (in a companion paper) are predicted using the proposed model. It is shown that the proposed model provides a close fit to the experimental results.