Low Yield Point Steel Research Articles

Cyclic hardening and softening behavior of the low yield point steel BLY160: Experimental response and constitutive modeling

The ability to model the cyclic behavior of low yield point steel accurately is essential for its application to seismic design. In this study, uniaxial tests of monotonic and strain controlled cyclic loading are conducted to investigate the mechanical properties of the low yield point steel BLY160. As observed in the test, work-hardening is an important hysteretic characteristic, which significantly influences the energy dissipation capacity of the steel. However, the cyclic softening in both stiffness and stress evolve as the plastic strain accumulates, which is manifested in the decrease of both the stress amplitude and the elastic domain of the stress–strain hysteresis loops. This change in the shape of the cyclic loops is called the “flattening effect” in this paper. To describe the cyclic hardening and softening effect by using one unified set of material parameters, a more sophisticated model based on the concept of internal variables is proposed as an extension of the combined isotropic-kinematic hardening model. The novel idea of a “transformation zone” with the introduction of an additional internal variable is proposed to synchronize the updates of isotropic and kinematic hardening such that the simultaneous change in the stress amplitude and the elastic region can be reproduced. Note that the cyclic softening develops in three stages: incubation, growth and the stabilization period. The logistic function, which presents a curve with an “S” shape, is first used to trace the evolution of the softening. Finally, the model parameters are identified by the test data, and the accuracy of the proposed model is verified by comparing the simulated performance and the experimental response under different loading histories. The results demonstrate that the extended model can elaborately describe the evolutional processes of cyclic hardening and softening by incorporating characteristics, such as the nonlinear transient behavior from elastic to plastic status, early yield under reversed loading and strain history dependence.

Constitutive Model of Low-Yield Point Steel and Its Application in Numerical Simulation of Buckling-Restrained Braces

AbstractLow yield point (LYP) steel is a kind of excellent material used in seismic structures. To get its constitutive model under cyclic loading, 20 specimens made of LYP steel SLY100 were tested under different loading systems. Monotonic characteristics, hysteretic curves, and failure modes were analyzed. Skeleton curves under cyclic loads were fitted. Parameters of combined hardening model were calibrated and verified. Then the constitutive model was applied in the numerical simulation of BRBs. It was indicated that SLY100 steel exhibited significant cyclic hardening phenomena and possessed distinguished ductility even after being subjected to cyclic loading. The Ramberg-Osgood model fit the skeleton curves well under cyclic loading with strain increasing gradually; good consistency between the stress–strain curves calculated by ABAQUS and test curves demonstrated the accuracy of the hardening parameters proposed. The finite element (FE) model of the buckling-restrained braces (BRBs) with SLY100 steel...

Structural performance of unstiffened low yield point steel plate shear walls

Employment of low-yield stress steel plates in shear wall systems has been demonstrated in a number of studies to be a promising alternative for improving the buckling stability, energy absorption capacity, and serviceability of these lateral force-resisting systems, in which material yielding of infill plates may occur either before or after or even at the same time as geometrical buckling. Accordingly, based on their slenderness parameter as well as buckling and yielding behavior, infill plates in steel shear wall systems may be divided into slender, moderate, and stocky categories with respective early buckling, concurrent buckling and yielding, and early yielding characteristics. Such a classification enables the accurate evaluation of buckling and yielding behavior of low yield point steel plate shear walls, which can consequently result in efficient structural and economical design of these lateral force-resisting as well as energy dissipating systems. On this basis, this paper assesses the structural behavior as well as plate–frame interaction characteristics of unstiffened low yield point steel plate shear wall systems via finite element and analytical approaches. Following the experimental validation of the numerical modeling, advantages of use of low yield point steel as compared to the conventional steel are demonstrated. Subsequently, the structural performances of code-designed shear walls with slender, moderate, and stocky low yield point steel infill plates are evaluated comparatively. Finally, the effectiveness of a modified plate–frame interaction (PFI) model in predicting the response of steel shear wall systems with moderate and stocky infill plates is demonstrated.

Hysteretic characteristics of shear panel damper made of low yield point steel

This study aims to identify the failure mode and hysteretic characteristics of shear panel damper made of low yield point steel (SLY120). The failure mode of shear panel damper is different depending on the width-to-thickness ratio (d/t) parameter. Quasi-static cyclic loading test was carried out on four different d/t ratio shear panel damper specimens. The non-linear finite element analysis was conducted using ANSYS LS-Dyna. The finite element analysis results were in good agreement with the experimental hysteresis curve.

Seismic design and behavior of low yield point steel plate shear walls

Steel plate shear walls (SPSWs) with low yield point (LYP) steel infill plates have been demonstrated in a number of studies to be efficient and promising lateral force-resisting and energy dissipating systems. In fact, use of LYP steel with extremely low yield stress and high elongation capacity compared to the conventional steel enables the employment of infill plates with improved buckling stability, serviceability, and damping characteristics. In contrast to the commonly-used slender and conventional steel plates with relatively low buckling and high yielding capacities, LYP steel plates can have low yielding and high buckling capacities due to the early yielding of the steel material. On this basis, this paper aims at evaluating the structural behavior and performance of SPSWs with unstiffened LYP steel infill plates designed per AISC 341 seismic provisions which typically address SPSWs with slender infill plates. Effects of plate aspect ratio, and combined compressive and shear forces acting on the web plate are also considered in this study. Numerical analysis of the code-designed LYP steel shear wall models demonstrates the efficient strength, stiffness, and cyclic performances of such systems. In addition, the effectiveness of some design requirements specified in AISC 341 code is evaluated based on the behavior of the SPSW components, and design recommendations are provided accordingly. Finally, a modified plate-frame interaction (PFI) method is used to predict and characterize the behavior of SPSW systems with low yielding and relatively high buckling capacities, the effectiveness of which is verified by comparing the predicted response with experimental and numerical results.

Seismic behaviors of steel plate shear wall structures with construction details and materials

In order to have a systematic and comprehensive comparison of seismic behaviors of steel plate shear wall structures with different construction details, a numerical method was proposed, which was proved accurately to predict the performance of structures with published quasi-static tests. Then, eight typical steel shear wall models with different structural construction details were established. Also an advanced stiffened low yield point steel plate shear wall was proposed to avoid excessive out-of-plane deformation. The seismic behaviors of above nine shear wall models were fully compared and analyzed, and key issues, such as energy-dissipating capacity, ductility, out-of-plane deformation and the effect of tension field on the columns were discussed in depth. The results showed that: in high-intensity seismic area, load-carrying capacity, hysteretic behaviors, failure modes, seismic ductility and economic performance should be taken into account comprehensively to choose the appropriate form of steel plate shear wall structure; the proposed low yield point steel plate shear wall with T type stiffened ribs could most effectively improve the energy dissipation capacity and ductility, and lessen the impact of tension field on the columns, besides, it had better load-carrying capacity and smallest out-of-plane deformation. This method provided a good way for improving the seismic behaviors of steel shear wall structures.

Seismic Performances of Replaceable Steel Connection with Low Yield Point Metal

Compared with the traditional steel rigid connection, the beam-column connections with weakened beam end have better ductility, but the local buckling in the weakened zone and the overall lateral deformation may occur in strong earthquake. The replaceable steel connection with low yield point metal is proposed based on the concept of earthquake resilient structure. In this connection, the weakened parts in the flange slab and web plate are filled with low yield point metal, and the metal firstly yields and dissipates energy sufficiently in earthquake; hence, the main parts are intact and the yield point metal can be replaced. The seismic performances of the three types of connections which include traditional connection, beam end weakened connection, and replaceable connection with low yield point steel under low cycle reciprocating load are studied. In addition, the energy dissipation capacity and damage characteristics of different connections are compared. The multiscale finite element models for the steel frames with different connections are analyzed by time-history method; both the computational efficiency and the accuracy are assured. The analysis results approve that the replaceable connection can confine the major damage in the replacement material and have better energy dissipation ability, safety reserves, and resilient ability.

Probabilistic assessment of structures with SPSW systems and LYP steel infill plates using fragility function method

Steel plate shear walls (SPSWs) have been used as primary lateral force-resisting systems in seismic design of new and retrofit of existing buildings. Employment of low yield point (LYP) steel infill plates with considerably low yield strength and high ductility, on the other hand, has been shown in a number of studies to improve the structural performance of SPSW systems. By considering the various sources of randomness and uncertainties involved in the design and retrofit process, adoption of a probabilistic methodology can result in a robust seismic performance assessment of such structural systems. This paper presents the results of a study on the seismic performance and vulnerability of retrofitted structures employing SPSW systems and LYP steel material through probabilistic seismic demand analysis (PSDA). Three 9-story code-designed and retrofitted structural models including a moment-resisting and two SPSW frames are considered. Appropriate seismic response and ground motion intensity parameters, and damage as well as repair states are selected. Structural and nonstructural drift and acceleration fragility functions are subsequently developed based on nonlinear time-history analysis results. The effectiveness of SPSW systems in improving the seismic performance and reducing the vulnerability of buildings is demonstrated through seismic response assessment and fragility analysis. Also, it is shown that employment of relatively thicker LYP steel infill plates in seismic design and retrofit of SPSWs results in smaller damage potential and better seismic performance of such systems.

Buckling and yielding behavior of unstiffened slender, moderate, and stocky low yield point steel plates

Steel plates may be classified as slender, moderate, and stocky based on their distinctive behavior characterized by geometrical buckling and material yielding. Slender plates undergo elastic buckling first and then yield in the post-buckling stage, while stocky plates yield first and then undergo inelastic buckling. Moderate plates, on the other hand, buckle and yield simultaneously. The development of low yield point (LYP) steel enables the application of steel plates with improved buckling and energy absorption capacities as lateral force-resisting and energy dissipating elements in structures. On this basis, buckling and yielding behavior of LYP steel plates with various support and loading conditions is studied in this paper from the point of view of their application in steel plate shear wall (SPSW) systems. The limiting thicknesses of standalone plates corresponding to concurrent geometrical buckling and material yielding are determined theoretically and verified through detailed numerical simulations. Effects of using LYP steel and plate aspect ratio parameter on the required limiting plate thickness as an effective parameter in seismic design of SPSW systems are investigated as well. In addition to the studies on the performance of plates with two and four restrained edges and also applicability of some extrapolation techniques for predicting the critical buckling load of moderate plates, detailed studies are performed on determination of the limiting plate thickness in code-designed SPSW systems. Based on the findings of this study, some practical recommendations are provided for efficient seismic design of SPSW systems with LYP steel infill plates.

Experimental study of reinforced concrete and hybrid coupled shear wall systems

Two approximately half-scale four-story coupled shear wall specimens were tested under both gravity and lateral displacement reversals. Specimen CW-RC, featuring traditional reinforced concrete (RC) shear walls and RC coupling beams, sustained ductile hysteretic response up to 3.00% drift. Specimen CW-S, featuring RC shear walls and steel coupling beam with low yield point steel (LYP) web, failed after completion of 2.00% drift cycles. The proposed connection detailing between the steel coupling beam and RC shear wall worked well in Specimen CW-S. Research results indicate that a ductile coupling beam design does not guarantee a ductile behavior of a coupled shear wall system. RC shear walls should be proportioned for axial and shear based on the provided coupling beam capacities. Design recommendations are provided.

The Statement of Research Progress in Embedded Steel Plate Shear Wall

Shear wall is the main component that resists the lateral force for high-rise buildings. With the rapid development of high-rise buildings, especially the super high-rise buildings, requirements for seismic performance of shear walls have become more sophisticated. This introduction summarizes the commonly used in embedded development and existing problems of steel plate shear wall, which are stiffened steel plate shear wall, non-stiffened steel plate shear wall, composite steel plate shear wall, preventing buckling of steel plate shear wall and low yield point steel plate shear wall.

Hybrid buckling-restrained braced frames

Structural systems that are available in building codes are calibrated for good performance at severe performance objectives (like life safety) under high earthquake hazard levels. However, building performance under low earthquake hazards is uncertain. The optimum seismic structural performance depends directly on the ability of stable hysteretic energy dissipation of ductile systems. This paper introduces a new structural steel system called hybrid buckling-restrained braced frame (BRBF). The “hybrid” term for the BRBF system comes from the use of different steel materials, including carbon steel (A36), high-performance steel (HPS) and low yield point (LYP) steel in the core of the brace. Nonlinear static pushover and nonlinear incremental dynamic analyses were conducted on a variety of BRBF models to compare the seismic behavior of standard and hybrid BRBF systems. Hybrid BRBF systems are shown to have a significant improvement over standard BRBF systems in terms of various damage measures including a significant reduction in the problematic residual displacements of the standard BRBFs.

Effect of fiber angle on LYP steel shear walls behavior

Steel shear wall (SSW) was properly determined using numerical and experimental approaches. The properties of SSW and LYP (low yield point) steel shear wall (LSSW) were measured. It is revealed that LSSW exhibits higher properties compared to SSW in both elastic and inelastic zones. It is also concluded that the addition of CFRP (carbon fiber reinforced polymers) enhances the seismic parameters of LSSW (stiffness, energy absorption, shear capacity, over strength values). Also, stress values applied to boundary frames are lower due to post buckling forces. The effect of fiber angle was also studied and presented as a mathematical equation.

Effects of using low yield point steel in steel plate shear walls

Steel plate shear walls are lateral load resisting systems, especially against earthquake excitation. They are constructed with or without stiffeners. Stiffened walls are more ductile than those without stiffeners. In this research a numerical study using finite element analysis via a finite element program is conducted. Nine thin steel plate shear wall models were considered in three groups of 5-storey, 10-storey and 15-storey walls. In each group different yield point steel for the infill plate was used. The yield points of infill plates were assumed to be 160, 200 and 240 MPa. The results showed that using low yield point (LYP) steel will increase energy dissipation of models by up to 63%. Using LYP steel also decreases the lateral displacement of models by up to 16%.

Hysteresis Characteristics of Shear Panel Damper Using SLY120

Shear panel dampers (SPD) are a type hysteresis damper used in structures to absorb seismic energy whereby damages to the major structural components could be minimized. It dissipates seismic energy by metallic deformation of the panel, welded between two plates called flanges and upper and lower end plates; and fatigue resistance around the welding part. The disadvantage of such dampers is that they absorb seismic energy only when they go through inelastic deformation. To overcome this restriction of hysteretic dampers, low yield strength steel is used as the material for hysteretic damper because low yield point steel has excellent ductility performance. Nonlinear finite element analysis was carried out to predict the large deformation and hysteretic behavior of SPD using low yield point steel (SYP120). The developed nonlinear SPD analysis model was verified with quasi static loading test.

Inelastic Shear Buckling Strength of Low-Yield-Point Steel Shear Wall

The mechanical properties of low-yield-point (LYP) steel and its advantages as seismic steel are introduced in this paper. The theoretical equations of inelastic shear buckling stress at the pure shear action for the LYP steel are derived from unified theory of plastic buckling. The relationship curve of inelastic shear buckling strength and width-thickness ratio of LYP steel shear wall at the different height-width ratios of plate is given through iteration calculation process. The effectiveness of theoretical equations used for calculating the buckling stress is verified by experimental results.

Energy dissipation system for earthquake protection of cable-stayed bridge towers

For economical earthquake resistant design of cable-stayed bridge tower, the use of energy dissipation systems for the earthquake protection of steel structures represents an alternative seismic design method where the tower structure could be constructed to dissipate a large amount of earthquake input energy through inelastic deformations in certain positions, which could be easily retrofitted after damage. The design of energy dissipation systems for bridges could be achieved as the result of two conflicting requirements: no damage under serviceability limit state load condition and maximum dissipation under ultimate limit state load condition. A new concept for cable-stayed bridge tower seismic design that incorporates sacrificial link scheme of low yield point steel horizontal beam is introduced to enable the tower frame structure to remain elastic under large seismic excitation. A nonlinear dynamic analysis for the tower model with the proposed energy dissipation systems is carried out and compared to the response obtained for the tower with its original configuration. The improvement in seismic performance of the tower with supplemental passive energy dissipation system has been measured in terms of the reduction achieved in different response quantities. Obtained results show that the proposed energy dissipation system of low yield point steel seismic link could strongly enhance the seismic performance of the tower structure where the tower and the overall bridge demands are significantly reduced. Low yield point steel seismic link effectively reduces the damage of main structural members under earthquake loading as seismic link yield level decreases due their exceptional behavior as well as its ability to undergo early plastic deformations achieving the concentration of inelastic deformation at tower horizontal beam.

Effect of Width-to-Thickness Ratio on Large Deformation in Shear Panel Hysteresis Damper Using Low Yield Point Steel

Recently, building and other civil engineering structures are built with energy dissipating device in order to reduce the damages caused by earthquake. There are a number of seismic energy dissipating device and steel dampers are among many energy dissipation device which is widely used because they are easy for construction, maintenance and low cost. Shear panel damper (SPD) is a type steel damper that dissipates energy by metallic deformation or using hysteresis of material as a source of energy dissipation. Low yield point steel is a good material to be used as a hysteresis damper since it has excellent ductility performance. Nonlinear finite element analysis was carried out to predict the large deformation and hysteretic behavior of SPD using low yield point steel (SLY120) for different width-to-thickness ratio. In order to verify the analysis simulation, quasi-static loading was also conducted and from the comparison a satisfactory result was found.

Experimental Study on Seismic Behavior of High Strength Steel Composite K-Type Eccentrically Braced Frames

High strength steel composite K-type eccentrically braced frame is a new structural system, in which the link is made from low yield point steel and the others are made from high strength steel. In order to study the seismic behavior of such a structure, four one-bay one-story 1/2 scaled plane specimens were tested under the monotonic and cyclic load respectively. The failure modes and the main indexes of seismic behavior of specimens with various links length were analyzed. The results show that this new structural form is good at energy dissipation and ductility, and the way of energy absorbing by shear yield is better than by flexure yield. Under cyclic load, the main failure were concentrated at links, while the other parts of the eccentrically braced frame kept in elastic status. This kind of structure is an excellent dual resistance system and easy to rehabilitate after earthquake.

New experimental system for base-isolated structures with various dampers and limit aspect ratio

A new experimental system of base-isolated structures is proposed. There are two kinds of dampers usually used in the base-isolated buildings, one is a viscous-type damper and the other is an elastic-plastic hysteretic-type damper. The base-isolated structure with a viscous damper and that with an elastic-plastic hysteretic damper are compared in this paper. The viscous damper is modeled by a mini piston and the elastic-plastic hysteretic damper is modeled by a low yield-point steel. The capacity of both dampers is determined so that the dissipated energies are equivalent at a specified deformation. When the capacity of both dampers is determined according to this criterion, it is shown that the response of the base-isolated structure with the elastic-plastic hysteretic damper is larger than that with the viscous damper. This characteristic is demonstrated through the comparison of the bound of the aspect ratio. It is shown that the bound of aspect ratio for the base-isolated structure with the elastic-plastic hysteretic damper is generally smaller than that with the viscous damper. When the base-isolated structure is subjected to long-duration input, the mechanical property of the elastic-plastic hysteretic damper deteriorates and the response of the base-isolated structure including that damper becomes larger than that with the viscous damper. The effect of this change of material properties on the response of the base-isolated structure is also investigated.