Low Yield Point Steel Research Articles

Double Low‐Yield‐Point Steel Corrugated Plates as an Innovative Damper to Improve the Behavior of CBF Braces

ABSTRACTIn this paper, an innovative damper made of low yield point (LYP) steel compound of double corrugated plate and flange plates to form an I‐shaped damper was considered parametrically and numerically. This damper pertain to easy fabrication and replacement after a severe earthquake. The proposed damper is expected to yield while elements outside the damper remain elastic. Consequently, it acts as a ductile fuse that was confirmed in this study. Results indicated that changing the damper from conventional steel to LYP steel improves the damper's performance. Because dampers with the same exhibited different responses, classification of the damper response based on the is not approritae. Of course, considering the fact that it has shear behavior with can be used in the initial design, but it is an incomplete criterion. Also, for dampers with , the ultimate strength is increased related to the from 2.64 to 4.50 times whereas for and is reached 1.35 to 3.84 times and 1.34 to 3.80 times, respectively. It confirms that on the , the most effective on the ultimate strength is obtained by changing the A36 steel to LYP steel. It should be noted that by increasing the by two to four times, the energy dissipation is enhanced 1.44 to 5.64 times for LYP dampers and 1.15 to 2.02 times for A36 dampers.

Cyclic behavior of improved low-yield point steel plate shear walls with T-shaped stiffeners

Based on the demand for high-performance lateral force-resistance systems for high-rise buildings, a new stiffened low-yield point (LY) steel plate shear wall (SPSW) structure is proposed. The infill plate is made of LY steel, and the stiffeners adopt a T-shaped section with greater flexural stiffness. Quasi-static tests are conducted on one unstiffened low-yield point steel plate shear wall (L-SPSW) and two stiffened L-SPSWs (using T-shaped cross and diagonal stiffeners). The cyclic behaviors of the L-SPSWs are compared through failure mode, damage development, hysteresis performance, and deformation performance. Numerical models are established and validated through experimental results. Finally, the performance of L-SPSWs with T-shaped and plate-type stiffeners is analyzed. The results show that the T-shaped cross stiffeners have the greatest enhancement in energy dissipation capacity (EDC) and stiffness, as well as the strongest suppression of the out-of-plane deformation (OPD) of the whole plate. T-shaped diagonal stiffeners have the greatest impact on enhancing the bearing capacity. It is suggested to strengthen the weld quality or select a steel material with LY for the diagonal stiffeners to ensure ductility. The use of T-shaped stiffeners can maximally improve the restraining effect on the OPD of the infill plate by 38.1 % compared with plate-type stiffeners.

Research on enhancement of low yield point steel pipes by fiber composite materials

This paper mainly studies on enhancement of low yield point steel pipes by fiber composite materials. By conducting compression tests on five specimens of fiber-steel pipe mortar columns (FSPMCs), the failure modes and load deformation relationships of the specimens are discussed. Based on the properties of specimens, further finite element analysis is conducted. The comparison of the results shows that the finite element analysis is in good agreement with the test results. Furthermore, parameter analyses are conducted on the different layers and overlapping allowances of aramid fiber reinforced plastic (AFRP) and carbon fiber reinforced plastic (CFRP). It is found that the bearing capacity of fibers on steel pipe mortar columns increases with the increase of fiber layers, and increases with the decrease of overlapping allowances. The bearing capacity of CFRP-wrapped steel pipe mortar columns is about 1.1–1.5 times that of AFRP. When the overlap allowance is 0°, the bearing capacity of CFRP is 19.1 % higher than that of AFRP. In addition, this paper proposes a calculation method for the bearing capacity of FSPMCs. The results show that the error rates between the theoretical calculation results and the test results are within 6 %, indicating that the proposed method has sufficient accuracy and can provide valuable references for subsequent research and engineering applications.

Ductile Fracture Prediction Framework of Low Yield Point Steel LYP225 under Monotonic Loading: Experiment and Simulation

Ductile Fracture Prediction Framework of Low Yield Point Steel LYP225 under Monotonic Loading: Experiment and Simulation

Hysteretic behavior of the segmented buckling‐resistant braces with LYP160

AbstractThe goal was to evaluate the hysteretic performance of buckling‐resistant braces with low yield point steel LYP160, the monotonic tensile and cyclic loading tests of LYP160 test specimens were conducted and the cyclic constitutive relationship was obtained. According to the load–displacement curves of the specimens, the low‐yield point steel was characterized by good ductility and energy absorption ability. With consideration of the Chaboche model for the materials, the cyclic hardening parameters of low‐yield point steel were obtained. On this basis, the hysteretic properties of buckling‐resistant braces under cyclic loads were simulated and analyzed. After the analysis and comparison of buckling‐resistant braces specimens with isotropic core plate and segmented variable section core plate, it can be found that: when the conventional buckling‐resistant braces with an isotropic core plate were loaded to L/100, the lateral deformation of the buckling‐resistant brace (BRB) would reach 17 mm. Additionally, serious squeezing could be observed on the lateral restraining members. The conventional BRB would become ineffective due to the accumulation of deformation at both ends of the BRB. When the segmented buckling‐resistant brace was applied, the core plate with variable section would buckle first in the middle area, other parts could continue to consume energy thanks to the action of the limit plate. It would avoid the situation that other areas would be unable to consume energy after the core plate yields at one area first. Under the action of cyclic loads, no stiffness degradation was noted in the segmented buckling‐resistant brace. Segmented buckling‐resistant braces demonstrated superior ductility and energy dissipation capacity.

A novel constitutive model for S30408 stainless steel considering strain memory effect: Formulation and implementation

To predict seismic behavior of steel structures and conduct performance-based seismic design, a precise constitutive model to accurately reflect the elastic-plastic response of structural steel under various loading protocols is always needed, so that the strength, deformation capacity, and energy dissipation capacity of a steel component or system in case of a severe earthquake can be reasonably evaluated. On the other hand, the constitutive model should be convenient for practical engineering implementation and application. Previous studies show that certain type steel like stainless steel S30408 shows complex features under various strain ranges such as pronounced strain memory effect, unsaturated cyclic softening/hardening under small/large strain amplitudes, which differ from mild steel and low yield point steel. Therefore, the stainless steel S30408 is taken as the research object in this study to develop a new constitutive model to describe structural steels with such complex mechanical properties. First, a new nonlinear isotropic and kinematic hardening rule is extended based on the classical Chaboche model and a functional relationship between the hardening rate (defined as the variation value of peak stress in every adjacent cycle during cyclic loading) and the applied strain amplitude is established through a logistics function to describe the coupling effects. Second, the numerical implementation technique for three-dimensional is elaborated in detail. Third, the numerical implementation technique is extended to plane stress cases by the improved P projection method. Using the numerical integration algorithm, the proposed constitutive model can be successfully incorporated into ABAQUS/Standard through the UMAT subroutine interface which is suitable for both solid and shell elements.

Methodical Investigations on Seismic Retrofitting of Steel Plate Shear Wall Systems

An efficient retrofitting technique is expected to improve the seismic performance of a lateral force-resisting system without increasing the seismic demand on the structure, which can unfavorably lead to irreparable damages during a seismic event. On this basis, the present study aims to introduce an optimal strategy for seismic retrofitting of steel plate shear wall (SPSW) systems using low yield point (LYP) steel material and to demonstrate its effectiveness through systematic investigations. To this end, detailed nonlinear static, cyclic, and dynamic analyses, as well as fragility analyses, have been performed on single- and multi-story, code-designed as well as retrofitted SPSWs. The aim is to identify the most efficient retrofitting approach and to demonstrate its effectiveness in enhancing the seismic performance and lowering the seismic vulnerability of the system. It is shown that replacing the original, conventional steel infill plate in an SPSW system with an LYP steel plate having twice the original thickness can improve not only the buckling capacity and serviceability, but also the structural performance and seismic response of the system, without increasing the demand on the structure and creating overstrength concerns. Fragility analysis also shows that the vulnerability, as well as probability, of damage to system can be considerably lowered as a result of the implementation of such a retrofitting strategy.

Enhancing the seismic performance of a concentrically braced reinforced concrete frame using an I-shaped shear link made of low yield point steel

Enhancing the seismic performance of a concentrically braced reinforced concrete frame using an I-shaped shear link made of low yield point steel

Hysteretic behavior of replaceable low yield point steel links with corrugated web

To develop a new replaceable steel link with high energy dissipation capacity for establishing a rapid recoverable system of bridge piers, a novel demountable and replaceable low yield point steel links with corrugated web (LCSW link) is proposed. A series quasi-static test on six specimens was conducted to investigate their failure process and hysteretic behaviors, considering the effects of different material and shape of the webs, as well the height-to-span ratio of the replaceable link. The experimental results indicate that the LCSW links exhibit three types of failure modes: the local buckling of steel flanges, the welding fracture at flange-to-endplate connection, and the combination of welding fracture at flange-to-endplate connection and shear buckling of CSWs. The hysteretic behaviors of the specimens were mainly affected by the height-to-span ratio. Moreover, utilization of a small height-to-span ratio (1.7 in this paper) and low yield point steel (LYP160 steel) in the links improves the ductility and energy dissipation capacity. Three-dimensional nonlinear finite element models were established to simulate the hysteretic behavior of the LCSW links, and the yield strength and initial stiffness of the LCSW links under lateral loading were obtained through finite element simulation and simplified design method. The comparison of experimental and analytical results indicates that the finite element models were able to simulate the cyclic response well, and these proposed theoretical equations can be used efficiently to predict the capacity of LCSW links.

Investigation of the performance of the self-centering steel plate shear wall considering stress relaxation in pre-stressed cables

Self-centring systems are one of the novel earthquake-resistant systems that can eliminate permanent earthquake-induced damage in buildings. In these systems, damage can be limited to those members that can be easily replaced after earthquakes. Self-centring steel plate shear walls (SC-SPSW) with pre-stressed cables combine the lateral load-resisting capacity of conventional SPSWs with the self-centring capabilities of PT beam-to-column connections and provide sufficient ductility and stiffness for the system. The stress relaxation phenomenon in pre-stressed cables can lead to stress reduction in cables with the passage of time. This phenomenon should not be neglected. In this study, the self-centering steel plate shear wall is simulated using finite element (FE) modeling and verified based on available experimental results; then, the effect of stress relaxation on stiffness and energy dissipation capability of the system is evaluated at different initial pre-stressing forces and time intervals. According to the results, after five years and for cables with a pre-stressing ratio of 0.7, the stiffness and dissipated energy have reduced by 26 and 5 percent, respectively, in comparison to the time just after pre-stressing. These values was 40 % and 2 % for stiffness reduction and energy dissipation capacity reduction, respectively when the cables were pre-stressed with the pre-stressing ratio of 0.9. Furthermore, A method is also suggested to improve the seismic performance of the self-centering connections which includes employing low yield point steel in energy dissipater devices. Results showed that the energy dissipation capacity of the system doubles by using low-point steel for the web plates. The cumulative dissipated energy was about 1.044 MJ with A1008 steel and it was increased to 2.058 MJ with LYP100 material. This increase was mostly observed after the 10th cycle of the hysteresis curve.

Resilient performance of steel connections with low yield point fuses considering the effect of RC floor slab

The beam-column connection of a steel frame equipped with replaceable low yield point steel cover plates (SF-LYCP) was proposed to address the significant repair challenge and financial losses caused by beam-column connection brittle failure after an earthquake. According to an experimental study, the SF-LYCP exhibited outstanding bearing capacity, ductility, energy dissipation, and post-earthquake rapid recovery performance. To explore the effect of the reinforced concrete (RC) floor slab on the mechanical behavior of SF-LYCP in a natural working environment, the finite element method of steel beam-column connection with low yield point (LYP) steel cover plates considering the effect of the RC floor slab (SF-LYCP-RCslab) was developed and analyzed by ABAQUS. The results demonstrated that the proposed finite method was able to accurately predict the behavior of SF-LYCP-RCslab. The load capacity, initial stiffness, and energy dissipation capacity of the SF-LYCP-RCslab were increased in comparison to the SF-LYCP. The LYP cover plates in the SF-LYCP-RCslab still played the desirable role of structural fuses. However, the concrete of the RC floor slab had severe damage and prevented the quick replacement of repairable LYP cover plates. Based on these findings, four improved strategies for the SF-LYCP-RCslab were proposed to reduce concrete damage and increase the replacement convenience of damaged elements. Comprehensively considering the bearing capacity, ductility, energy dissipation, structural fuse function, concrete damage, and post-earthquake rapid recovery performance, the improved strategy, which adopted a profiled steel–concrete composite floor slab with a gap, was recommended in steel frame beam-column connection design.

Research on high‐performance steel structure with high‐strength steel column, ordinary‐strength steel beam, and low‐yield‐point steel BRB

AbstractIn order to reasonably make full use of the advantages of different steels and then achieve a steel structure with excellent seismic behaviour, the authors proposed novel triple grades hybrid high‐performance steel structures (TGHSSs) comprising high‐strength steel (HSS) columns, ordinary‐strength steel beams, and low‐yield‐point (LYP) steel buckling‐restrained braces (BRBs). The basic concept and expected advantages were introduced. To validate this concept, eight full‐scale single‐bay two‐storey TGHSS specimens were tested under cyclic loads, in which columns are of 460 MPa, 690 MPa, and 890 MPa HSSs, beams are of 345 MPa steel, and BRBs are of 100 MPa, 160 MPa, and 225 MPa LYP steels. Meantime, nine LYP steel BRB specimens were taken out and tested under uniaxial cyclic loads. Based on the experimental study, numerical simulation and parametric analyses on TGHSSs were further conducted, and a performance‐based design method was proposed. Results indicated that the TGHSSs featured a sequential yielding mechanism with excellent seismic performance. Specifically, the LYP steel BRBs yielded at first to dissipate seismic energy. Then, the ordinary‐strength steel beams developed plastic hinges at beam ends. At last, the HSS columns kept almost elastic or presented limited plasticity at column bases. This research proves such a high‐performance structure with a reasonable combination of high, ordinary, and low strength steels, whose advantages can be fully developed.

Experimental study on seismic performance of low-yield point steel plate shear walls

This paper studies the seismic performance of the low-yield point steel plate shear wall (LSPSW) by conducting cyclic loading tests on three single-story single-span steel plate shear wall (SPSW) specimens, including a non-stiffened LSPSW (LYP) and a non-stiffened normal strength SPSW (NW). A new LSPSW with steel tube stiffeners (HSS) is then proposed to restrain the out-of-plane deformation of the infill panel. The failure modes, strain development, bearing capacity, stiffness, ductility, energy dissipation capacity, degradation characteristics, and deformation performance of the above three SPSWs are compared and analyzed. Afterwards, the corresponding numerical modeling approaches are developed and verified by the test results. Furthermore, supplementary analyses of the plate-frame interaction in terms of the shear distribution, energy dissipation behavior, and plastic damage performance are performed, and relevant suggestions are provided for the design of SPSW. The experimental and numerical results show that compared with the NW specimen, the use of low-yield point steel in the LYP specimen significantly improves the ductility and energy dissipation capacity of the SPSW, delays the tearing of the infill panels, reduces the residual deformation of the infill panels with higher ability of recovery, and achieves a more uniform distribution of cumulative plastic deformation. The application of steel tube stiffeners in the HSS specimen further enhances the energy dissipation capacity of LSPSW, effectively restrains the out-of-plane deformation of the infill panels, and reduces the impact of the tension strips on the edge columns. The analyses of the plate-frame interaction show that the boundary frame has more contribution to the shear resistance and energy dissipation after using the low-yield point steels for the infill panel. The proportion of shear force borne by the boundary frame is up to 65%–70%, which should be considered in the design procedure to optimize the geometrical dimensions of the infill panel and the boundary frame, allowing to optimize the structural performance and material utilization.

Experimental study on bamboo-shaped buckling-retrained energy dissipater with different grades of steel

Buckling-restrained energy dissipaters are miniature energy dissipaters that constrain an inner core through an outer tube and have been widely utilized to improve the seismic performance of fabricated structures. Low yield point steel is often used to produce energy dissipaters, but the mechanical behavior of low yield point steel energy dissipater is rarely investigated. In this paper, a quasi-static test of bamboo-shaped energy dissipaters with different grades of steel was carried out. The influence of the material and configuration of the core on the fatigue performance and failure mode was evaluated. Test results showed that all specimens demonstrated stable hysteretic performance. The equivalent viscous damping ratio of low yield point steel energy dissipaters was relatively large at small strain amplitudes. At large strain amplitudes, both had a similar energy dissipation capacity. The compressive strength adjustment factors and strain hardening factors of low yield point steel energy dissipaters were higher because of their lower post-yield stiffness and significant isotropic hardening. The fracture mode on the low yield point steel energy dissipaters was similar to flat rupture, and significant necking was observed here. However, the normal strength steel energy dissipaters exhibited slant fracture, and no evident necking occurred. Two deformation modes were proposed. A calculation method for the buckling wavelength of the energy dissipater was proposed. When the effective length of the yielding region was smaller than the buckling wavelength, the fatigue performance of low yield point steel energy dissipater was better than that of normal strength steel energy dissipater, and the low yield point steel energy dissipater had a better reserve performance.

Seismic behavior of steel reinforced precast concrete shear wall with replaceable energy dissipators

To improve the seismic performance of the precast shear walls, a steel-reinforced precast concrete shear wall with replaceable low-yield-point (LYP) steel energy dissipators (SPCE-Wall) was developed. The design approach and analytical model of SPCE-Wall which applied equivalent fiber elements to simulate the steel-reinforced precast concrete panel and fiber element to simulate the LYP steel were adopted in the study. After validating the analytical finite model, the seismic behavior of the SPCE-Wall and parametric study were performed in OpenSees. The results indicated that SPCE-Wall exhibits an enhanced bearing capacity, energy dissipation capability and initial lateral stiffness under monotonic and cyclic loading compared with the steel-reinforced concrete wall without energy dissipators. The relative energy dissipation ratio of the SPCE-Wall exceeds 0.125, which satisfies the ACI ITG T5.1 recommendation to avoid the long-term oscillation of the structure resulting from inadequate damping. Parametric study analysis shows that the bearing capacity of the SPCE-Wall is affected by the axial compression ratio, length of the wall panel and the steel area including channel steel, steel bars and LYP plates. And the displacement ductility of the wall is considerably influenced by several structural properties including axial compression ratio, length of the wall and diagonal angle steel.

Cyclic behavior of hot-rolled titanium-clad bimetallic steel under large plastic strain reversals

Titanium-clad (TC) bimetallic steel is a versatile and high-performance material that offers a unique combination of different service properties, making it ideal for various engineering applications where both durability and strength are critical. Existing studies are exploring the application possibility of TC bimetallic steel in seismic zones. The severe seismic action tends to induce large-strain cyclic reversals in structural members. Thus, it is necessary to clarify the cyclic behavior of TC bimetallic steel under large-magnitude cyclic strains, whose strain range exceeds the strain level of conventional low-cycle fatigue tests. This paper has performed 7 large-strain cyclic coupon experiments on hot-rolled TA2 + Q355B TC bimetallic steel. The influences of different loading protocol on cyclic behaviors are clarified. All hysteretic stress-strain relations of TC bimetallic steel exhibit favorable plumpness under large-strain reversals. The increase in maximum strain and accumulation of plastic strain both induce apparent deterioration on elastic modulus. Based upon the experimental stress-strain relations, the Chaboche combined isotropic/kinematic hardening model parameters are calibrated and validated. The flow stresses of most tests exhibit little change over the full-range plasticity, illustrating that the isotropic hardening behavior is negligible. The cyclic behavior of TC bimetallic steel under large-strain reversals can be precisely simulated by a pure kinematic hardening constitutive model rather than a combined isotropic/kinematic hardening model. The Chaboche parameters calibrated from small-strain and mediate-strain cyclic loading tests tend to overestimate the hysteretic energy dissipation ability under large-strain reversals. In addition, the stress-strain relations of TC bimetallic steel are compared with those of low yield point steels, mild steels and high strength steels. The hysteretic energy dissipation ability of TA2 + Q355B TC bimetallic steel is greater than that of low yield point steels, but less than those of mild steels and high strength steels.

Investigation of the Behavior of Steel Plate Shear Walls Considering Double Corrugated Low-Yield-Point Steel Infill Plate

During the last three decades, interest in the application of steel shear walls has increased worldwide. Steel shear walls are used as stiffened and unstiffened walls. One of the main shortcomings of the steel plate shear wall (SPSW) is the infill plate buckling mainly under lateral wind and seismic loads. One of the useful solutions to prevent lateral buckling is the use of walls with corrugated plates. In this research, the behavior of a steel shear wall consisting of two corrugated plates was investigated in the two material cases of the conventional ASTM A36 steel and the low-yield-point (LYP) steel. The use of steel with low yield strength improves the seismic performance of the steel shear wall system. In this study, the effect of the corrugation angle and aspect ratio of the plate were investigated. The results showed that the effect of corrugation angle on the structural parameters of walls with LYP steel is greater than that of walls with A36 steel. By increasing the corrugation angle from 30° to 60°, the elastic stiffness of A36 and LYP walls decreased about 24 and 36%, respectively, and the response modification factor (Ru) of A36 and LYP walls decreased by about 24 and 56%. The corrugation angle has a lower effect on the ultimate strength and energy absorption. Investigating the effect of aspect ratio showed that increasing the aspect ratio improves the seismic performance of the wall.

Dynamic Mechanical Behavior at Elevated Temperatures and High Strain Rates of Low Yield Point Steels

Dynamic Mechanical Behavior at Elevated Temperatures and High Strain Rates of Low Yield Point Steels

A simplified prediction method on Chaboche isotropic/kinematic hardening model parameters of structural steels

The Chaboche combined isotropic/kinematic hardening model has gained wide popularity due to its outstanding description on cyclic stress-strain relations of different structural metals. However, the calibration on material parameters of Chaboche model needs to perform at least a cyclic loading test to gain the experimental data, leading to a considerable time and economic cost. To reduce such calibration expense, a simplified calibration approach was proposed in this paper. Firstly, the Chaboche model parameters of various structural steels, including low yield point steels, mild steels, and high strength steels, were calibrated based upon 171 experimental stress-strain curves by using an identical calibration procedure. Secondly, these parameters calibrated were correlated with the monotonic yield strength and fitted through suitable description formulations. Subsequently, a four-steps prediction method of Chaboche model parameters was proposed to replace the traditional complex calibration approach. Based upon the new prediction method, the values of all Chaboche model parameters can be directly obtained when monotonic yield strength is known. Furthermore, the simulation performance of this new prediction method was validated by comparing a series of simulation stress-strain relations with their experimental counterparts. The probabilistic distribution types of these parameters were accordingly identified and the corresponding statistical parameters were fitted. This study provides a simplified prediction method and a probabilistic description on different Chaboche model parameters, producing a foundation for random analysis of stress-strain behaviors on various structural steels.

Utilizing Low Yield Point Steel to Improve the Behavior of the I-Shaped Shear Links as Dampers

Concentrically braced frame (CBF) systems are susceptible to buckling (which causes a decrease in energy absorption), although this system has considerable lateral stiffness and strength. To over this shortcoming, researchers have suggested the use of I-shaped steel dampers as a practical idea that prevents buckling and increases the energy absorption but reduces the stiffness of the system. To increase the stiffness of the damper, the thickness of the web or the thickness of the flange can be increased, but by increasing their thickness the shear capacity of the damper also increases. Nevertheless, with the increase in the capacity of the damper, the forces created in the elements outside the damper will also increase, which is usually not a suitable solution. Therefore, in this paper, the use of the low yield point for the web plate of an I-shaped damper is proposed to compensate for it. Accordingly, its behavior is investigated parametrically and numerically and also requires equations to design the system proposed. Results indicated that utilizing an LYP damper improves the behavior of the system in the case of energy absorption, stiffness, and strength. Comparing the LYP damper and the conventional I-shaped damper (made of A36 steel) reveals that both dampers pertain to stable hysteresis loops without any degradation, which confirms the capability of the I-shaped damper to dissipate seismic energy. Although the flange plate properties contribute to the load-bearing of the damper, the A36 damper is more affected by the flange plate than the LYP damper that is concluded for LYP dampers the flange plate contribution in the shear strength of the damper is ignorable at the beginning of imposed loading.