High Axial Ratio Research Articles

Effect of high-strength steel spirals on the seismic behavior of square concrete-filled steel tubular columns under high axial load ratio

Ductility of square concrete filled steel tubular (CFST) columns is generally significantly lower than that of circular ones, especially when they are under high level of axial loads. Many previous studies suggested that adding internal steel spiral stirrups is an effective measure to improve ductility of square CFST columns. To investigate the effect of high-strength steel (HSS) spirals on the seismic behavior of the HSS spiral-confined CFST (HSS-CFST) columns under high axial load ratio, 15 square CFST columns, including 3 conventional CFST columns without internal steel spirals, 3 normal-strength steel (NSS) spiral-confined CFST (NSS-CFST) columns, and 9 HSS-CFST columns were experimentally studied through the cyclic loading tests. The critical test parameters included the steel spiral pitch and axial load ratio. Final failure modes, hysteretic response, skeleton curves, strain distributions, ductility, energy dissipation capacity, and stiffness degradation of the specimens were investigated in detail. The experimental results indicated that (i) apparent outwardly local bucking of the steel tube and core concrete crushing were observed for all specimens in the plastic hinge regions at the ultimate state; (ii) adding both the NSS and HSS spirals would beneficial in improving the hysteretic behavior and energy dissipation capacity of square CFST columns, but contributions to these improvements made by the HSS spirals were more significant than that of the NSS ones; (iii) the increase of axial load ratio and internal steel spiral pitch would impair the load-carrying capability and ultimate deformation ability of square CFST columns; (iv) ductility of the NSS-CFST and HSS-CFST columns could be improved as the increased of spiral volume ratio and the ductility enhancement was more pronounced in the HSS-CFST columns; and (v) the internal steel spirals were helpful in delaying the stiffness degradation rate of square CFST columns, particularly for those specimens under a high axial load ratio of 0.8.

Experimental study on the seismic behavior of RC columns with high axial compression ratios retrofitted by large rupture strain fiber-reinforced polymer

Fiber-reinforced polymer (FRP) composites being utilized to retrofit reinforced concrete (RC) columns has been well documented. However, the axial compression load of the FRP retrofitting RC columns was relatively limited. Aiming to analyze the applicability of FRP retrofitting RC columns with higher axial compression loads, this paper presents an experimental study on the seismic performance of RC columns retrofitted by the Polyethylene Terephthalate (PET) FRP composites. A total of twelve 1/3 scale RC columns were fabricated, including four control specimens and eight PET FRP retrofitting columns with two retrofit schemes. All the columns were tested under combined high axial compression load and cyclic lateral displacement excursions, and the maximum axial compression ratio reaches 1.1. The seismic performance of RC columns retrofitted by PET FRP was analyzed detailedly from the failure mode, shear force and deformation capacity, energy dissipation and ductility. The test results showed that PET FRP retrofitting changed the failure mode of RC columns from brittle to more ductile. The post-peak strength degradation of the columns was more rapid with the increase of axial compression ratio, but the strength degradation of the PET FRP retrofitting columns was more gradual. PET FRP retrofitting significantly improved the ductility and lateral deformation capacity of the columns even under the high axial compression ratio. PET FRP retrofitting can be applied for the RC columns with serous demand of deformation capacity due to the lighter change of shear-loading capacity and stiffness. Contrastively, the improvement of the seismic capacity of the RC columns retrofitted by the laterally wrapped scheme is higher than that of the striped wrapped scheme. Conclusions from this study provide useful references for the seismic retrofitting of RC structures.

Seismic performance of squat UHPC shear walls subjected to high-compression shear combined cyclic load

Cyclic tests of five UHPC squat shear walls and one high-strength concrete counterpart were carried out in this study to investigate the seismic performance of UHPC shear walls with high design axial load ratio ranging from 0.5 to 0.6, and web distributed reinforcement ratio varying from 0.19% to 0.56%. The failure mode, crack pattern, force–displacement relationship, deformation mechanism, energy dissipation, the strength and stiffness degradation are comprehensively investigated. In addition, the stress development and shear contribution of horizontal rebar in the web is calculated and analyzed. Finally, design suggestions for UHPC squat shear walls are proposed in terms of minimum horizontal reinforcement ratio and axial load ratio. It is demonstrated by the test results that UHPC specimens showed an excellent crack control ability with narrow shear-related cracks distributed in a dense array. The shear capacity and ultimate deformation of UHPC specimen were significantly improved by almost 85% and 95% in comparison with high-strength concrete specimen. Noticeably, the UHPC specimen with the minimum amount of transverse rebars reached the highest ultimate drift ratio of 1.75%. The stress level of horizontal rebars in UHPC specimens can be reduced by at least 72%. The test results show the potential to reduce the horizontal reinforcement ratio to 0.19% for the UHPC squat shear walls under the high design axial load ratio of 0.5. A modified strut-and-tie model for predicting the shear strength of UHPC shear walls is proposed with an error of no more than 4%.

Study on the seismic performance of regional confined concrete columns

This paper experimentally investigated the seismic performance of three regional confined concrete columns (RCCCs) and three normal confined concrete columns (NCCCs) subjected to low cyclic loading under a high axial compression ratio. The crack development and failure mode were studied. The effects of the axial compression ratio and stirrup form on the behavior (i.e., hysteretic behavior, stiffness, ductility and energy dissipation) of confined concrete columns were studied. The experimental results suggest that both NCCCs and RCCCs have good bearing capacity and ductility, and their failure modes are similar. At the same axial pressure ratio, the ductility and energy dissipation capacity of RCCCs are 5% and 10% higher than those of NCCCs respectively. The best load carrying capacity and energy consumption of the confined concrete columns are achieved when the axial compression ratio is 1.1. Furthermore, a finite element analysis was conducted to simulate the behavior of the RCCC. The results of the finite element analysis agree with the test results. The simulated results show that the peak load and cracking load of the RCCC decrease with increasing stirrup spacing.

Experimental study on seismic behavior of precast concrete sandwich shear walls under high axial compression ratio

To shed light on the seismic behavior of precast concrete sandwich shear walls (PCSSWs) in high-rise buildings, reversed cyclic loading test were conducted on eight full-scale shear wall specimens under high axial compression ratio. Totally four variables were considered in the test, i.e. type of shear wall (PCSSW, non-insulated precast concrete shear wall (PCSW), cast-in-place (CIP) shear wall), location of insulation layer (off-center or center in the section), confinement at boundary elements (with or without confined core), and details of grouted sleeve connection (double or single row of grouted sleeves). Note that in this paper the PCSSWs with off-centered insulation layer had confined cores at boundary elements while steel stirrups for additional confinement were not used in the PCSSWs with centered insulation. Test results revealed that the PCSSWs showed failure mode, hysteresis loops, loading capacities and displacement ductility similar to PCSW and CIP specimens. The loading capacities of PCSSWs and CIP specimen increased by 8.2 % ∼12.4 % because of the confined core at boundary elements. The displacement ductility of specimens with confined boundary elements varied from 2.35 to 2.65, which was higher than that of the specimens with unconfined boundary elements (1.75 ∼ 2.10). Besides, the number of rows of grouted sleeves had minor effect on hysteretic response of specimens. Based on the test results, a quadrilinear degradation restoring force model was proposed.

Seismic performance of a novel partly precast RC shear wall with double precast edge members and a central T-shape CIP member

A novel partly precast shear wall was proposed in this study to accelerate construction and further reduce the weight of precast components for high-rise building structures. The proposed wall consisted of double precast edge members and a central cast-in-place (CIP) member. The rebar splice was achieved by the grout-filled sleeve connection for the precast members and lap splice connection for the CIP member. The seismic performance of the proposed wall was investigated through a full-scale experimental program, in which three specimens were designed and tested under the combination of a constant axial load and cyclic loads, including two identical proposed walls and a CIP wall as a reference. The axial load was applied to achieve a high axial load ratio of 0.5. Based on the test results, it was found that the proposed walls were subjected to similar damage progression and failure mode with the CIP wall. All failed due to concrete crushing, shear cracking and rebar buckling at the base corners of walls. The only difference was that the proposed walls would experience additional vertical cracks along the interface between the precast and CIP zones due to insufficient bond strength between at the interface. It was also found that under the high axial ratio of 0.5, the proposed walls would have comparable seismic performance with the CIP wall in terms of deformability, ductility and lateral load capacity. In addition, the two identical proposed wall had similar seismic performance indicating the good repeatability of test data and stable performance of the walls. Therefore, the proposed walls can have satisfactory seismic performance during a seismic event and could be an effective alternative method for the CIP walls if designed appropriately.

Experimental Study on the Seismic Behavior of Squat SRC Shear Walls with High Axial Load Ratio

This paper aims to study the seismic behavior of squat steel-reinforced concrete (SRC) shear walls with a high axial load ratio. Nine squat SRC shear walls with varying axial load ratios, steel ratios, and horizontal distributed reinforcement ratios were tested under lateral cyclic reversed loading and an axial load. The failure process, load-deformation hysteretic response, shear strength, ductility, and the strain of the specimens are reported. The results show that all the specimens failed in shear with the crushing of the web concrete. No axial failure occurred after the web concrete was crushed since the boundary elements encased with structural steel sections maintained the axial load. Larger steel ratios reduced the buckling degree of the structural steel. A larger horizontal distributed reinforcement ratio was clearly beneficial for the ductility and energy dissipation capacity of the specimen, while it had a negligible effect on the shear strength. The Chinese code provided an extremely conservative prediction of the shear strength of the tested squat SRC shear walls with a mean calculated-experimental strength ratio of 0.42. An improved formula was established mainly by the modification of the shear resistance contributed by the concrete and the structural steel, leading to a mean calculated-experimental strength ratio of 0.74. More experimental data are still needed to establish more accurate deformation acceptance criteria for SRC shear walls and to promote the performance-based seismic evaluation of SRC structures.

Experimental Study on Seismic Performance of Prefabricated Frame Column Joints with a High Axial Compression Ratio

A new type of an assembled monolithic concrete column encased by partial outsourcing steel was proposed, and the seismic performance was proposed. To study the seismic performance such as failure mode, hysteretic behavior, deformation, ductility of the specimen, and the influence of the outsourcing steel pipe on the mechanical performance of the specimens, the comparative tests of four full-scale specimens under low cyclic reciprocating load under a high axial compression ratio were carried out. The test results show that the monolithic column assembled with outsourced steel has better overall performance, and the failure of the specimen is the large eccentric compression failure with good ductility. The hysteresis and skeleton curves of the assembled columns are similar to the cast-in-site concrete column under the same conditions, which have a good ductility and energy dissipation capacity. It was established that increasing the thickness of the outer steel plate does not significantly improve the mechanical performance of the component when the load-bearing capacity of members satisfies the design requirements. The research results can provide a reference for theoretical research and practical engineering applications of assembled monolithic concrete column connections.

Experimental and numerical study on seismic behavior of prestressed concrete composite shear wall

In this study, a novel type of prestressed concrete composite shear wall is proposed. The proposed shear wall consists of two precast prestressed concrete slabs with steel trusses and in-filled concrete. The thickness of this precast slab was reduced to 35 mm, and the weight was correspondingly reduced. The prestressed steel in the precast slab acted as horizontal steel in the composite shear wall, thereby improving the shear resistance of the composite shear wall. Four prestressed concrete composite shear walls and one cast-in-situ shear wall were tested under cyclic loading to study the seismic behavior. The seismic behaviors, including failure modes, hysteretic curves, stiffness degradation, and energy dissipation, are analyzed and compared. The effect of the type of boundary element on the composite shear wall was also examined. The test results revealed that the composite shear walls had almost the same seismic performance as the cast-in-situ shear wall. Compared with the cast-in-situ shear wall, the energy dissipation capacity of the composite shear wall was enhanced. The horizontal prestressed steel in the composite shear wall reduced diagonal crack propagation. Among the prestressed concrete composite shear walls, specimen PW1, whose boundary elements were completely cast-in-situ, exhibited better seismic performance. To investigate the effects of the axial compression ratio and initial prestress level on the seismic performance of the composite shear wall, a finite element model was established for the cast-in-situ shear wall and prestressed concrete composite shear wall. The analysis results indicated that under a high axial compression ratio, the bearing capacity and ductility of the composite shear wall were higher than those of the cast-in-situ shear wall. Under a higher axial compression ratio, the ductility of the composite shear wall improved as the initial prestress increased. Above all, the proposed prestressed concrete composite shear wall is suitable for practical projects.

Seismic performance of precast concrete column with different longitudinal reinforcement diameters under different lateral loading directions

To improve the installation efficiency of precast concrete (PC) columns with grouted sleeve connections, increasing the diameter of longitudinal rebar but keeping similar reinforcement ratio is a solution. To quantify the effects of longitudinal reinforcement diameter on the seismic performance of PC columns, eight full-scale reinforced concrete columns (six PC columns and two cast-in-situ) with identical concrete strength, reinforcement ratio, and stirrup ratio were designed and fabricated. The longitudinal reinforcement diameters varied from 18 mm to 32 mm. Moreover, considering majority of existing tests on PC column were subjected to relatively low axial compression ratio due to limitation of test facilities. Low-cyclic reversed loading tests were conducted with a high axial compression ratio of 0.6. Furthermore, to evaluate the bilateral loading effects, the loading direction was either horizontal or diagonal. Test results showed that the PC column achieved even higher lateral load capacity than corresponding cast-in-situ column regardless of the loading directions. Moreover, the lateral load capacity of the column under diagonal loading is generally lower than that under horizontal loading. However, the ductility and energy dissipation capacity of the columns under diagonal loading were higher than those under horizontal loading. Increasing the diameter of the longitudinal reinforcement will increase the lateral load capacity of the PC columns. This is because increasing the diameter of the longitudinal reinforcement required larger size of grouted sleeve, which further shortened the effective length of the column due to plastic hinge shifting. However, increasing the diameter of the longitudinal reinforcement may require greater bond strength between rebar and concrete and aggravate the bond failure pre-mature, which resulted in the less of deformation capacity and ductility, as well as energy dissipation capacity.

Axial load ratio and limit for ductility design of steel fiber-reinforced concrete composite shear walls

Serious compression failure of reinforced concrete shear walls under high axial load ratios can be effectively prevented by adding steel fibers at the bottom, combined with an imbedded steel profile in the boundary element. However, the existing axial load ratio limit for conventional reinforced concrete shear walls is not suitable for performance-based design of such composite structural member. The seismic behavior of three composite walls with different fiber volume fractions (0–2.0%) was investigated through experimental and numerical studies under the preliminarily determined axial load ratio limit. The influence of the axial load ratio and boundary element requirements on the displacement ductility was numerically quantified. Addition of fibers assisted in mitigating the crushing of bottom concrete, improving the displacement ductility, and maintaining the bearing capacity under large deformations. Subsequently, an axial load ratio limit relax of 0.1 to 0.2 was adopted for such walls with fiber volume fraction of 1.0% to 2.0% to obtain a displacement ductility consistent with traditional walls. Finally, the axial load ratio limit and corresponding requirements on boundary elements for such walls with separate ductility demand have been recommended, which can provide guidance for performance-based design of such composite walls with flexure-controlled failure mode, however, shear-controlled walls should also be investigated in further studies.

Effect of Fast Loading on the Seismic Performance of SRUHSC Frame Structures

Due to the high compressive strength and durability of ultra-high-strength concrete, SRUHSC (steel-reinforced ultra-high-strength concrete) frame structures have been used extensively in super-high-rise buildings. However, the SRUHSC showed obvious brittleness. Encasing structural steel in the material was recognized to be a good way of alleviating the problem of brittleness. The purpose of this study is to investigate the effect of the axial compression ratio on the seismic performance of a single-story, single-span SRUHSC frame structure under rapid loading. The failure mode, deformation, strength and stiffness degradation, energy dissipation capacity and residual displacement of the structure were compared and analyzed. The seismic performance of a single-story single-span SRUHSC frame structure is verified under the conditions of a fast loading rate and high axial compression ratio. The results suggest that the horizontal resistance capacity of structures can be significantly improved by fast loading in the elastic and elastic–plastic ranges. The ductility coefficient of the structure increases with the same axial compression ratio under fast loading. With an increase in loading rate, the secant stiffness of the structure is improved.

Experimental assessment of the residual capacity of axially loaded blast-damaged square RC columns

The aftermath of the Oklahoma City Bombing and the events of September 11, 2001 in the United States led to intense research into the response of infrastructure to explosion effects and the attendant risk of progressive collapse of building structures. The research has not addressed the residual capacity of blast-damaged columns. The challenge to structural engineers is determining the residual capacity of blast-damaged columns and deciding which should be demolished and which can be repaired cost-effectively. This paper presents the results of an experimental program designed to investigate the residual capacity of blast-damaged columns in the laboratory.The blast-damaged columns, from an earlier field test program, were first subjected to the design axial service load of 1000 kN. Columns capable of resisting the service load were subjected to additional lateral loading to determine their residual flexural capacity. The test results show that columns with reduced tie spacing exhibited higher post-blast residual capacity from the explosion at the same scaled distance. Also, a high axial load ratio was observed to adversely affect the flexural load capacity of the reinforced concrete columns in a numerical parametric analysis done using the finite element program LS-DYNA.

Torsional behaviour of tapered CFDST members with large void ratio

This paper investigated the mechanical behaviour of tapered concrete-filled double skin steel tubular (CFDST) members under combined axial compression and torsion. A series of experiments on CFDST specimens were tested including 8 tapered members and 2 normal members with various hollow ratios and axial compression ratios. The torsional performance of tapered members was analyzed on failure modes, torque-rotation angle curves, and torque-shear strain curves. Verified FE models were developed to carry out the full-range analysis, stress and strain distribution, and the contact stresses between the components. The results showed that the failure mode of tapered CFDST columns was the torsional deformation occurred between 0.5H and the top section. The specimens with a high axial compression ratio occurred additionally inclined outward buckling at 0.8H section, giving rise to a decline in torsional capacity. A low level of axial force promotes the torsional bearing capacity. The effects of the taper angle and hollow ratio on the distribution of shear strain and the torsional capacity at different heights are obvious. Furthermore, employing the section with the lowest torsional modulus for tapered CFDST members is conservative as the designed section, because the torsional capacity might be underestimated. Finally, a simplified method defined by a new calculated section for forecasting the torsional performance of tapered CFDST members is proposed.

Seismic behavior of an innovative equivalent monolithic precast shear wall under low and high axial load ratios

To meet the demands for the axial load and shear capacity of prefabricated reinforced concrete shear walls located at lower floors in high-rise buildings in high seismic intensity area, an innovative equivalent monolithic precast shear wall (labeled as EMPSW) was proposed by introducing X-shaped steel plate bracings and high ductility hidden column in this research. And seismic behavior of two EMPSWs under low and high axial load ratios (ALRs) were evaluated by quasi-static loading tests. The experimental phenomenon showed that EMPSWs under low and high ALRs presented similar fully developed and wide distributed cracks, whilst the ultimate draft ratios and ductility coefficients of specimens all met the specification requirements, exhibiting good lateral resistance through ductile damage for EMPSWs under different ALRs. Also, the increase of ALRs could improve the load carrying capacity and initial stiffness, but had no benefit on the energy dissipation and deformation capacity of EMPSW. Then, a reasonable strut-and-tie model (STM) was applied and verified to be well suitable for predicting the mechanical behavior of EMPSW. Besides, further investigations regarding the influence of critical parameters were implemented by finite element analysis (FEA). The FEA results illustrated that a higher ALR was beneficial for load-bearing capacity but had a significant negative impact on deformation capacity, thus the test ALR for EMPSW should be controlled within 0.5 in engineering practice. The volumetric ratio of X-shaped steel plate bracings and longitudinal reinforcement ratio in hidden column had a positive effect on capacity, but their contributions decreased as ALR increased.

Hysteretic behavior of precast concrete shear walls with steel sleeve-corrugated metallic duct hybrid connections

In this paper, a hybrid connection that incorporates grouted steel sleeve splices (GSS) and grouted corrugated metallic ducts (GCMD) for precast concrete shear walls (PCSWs) is proposed. This hybrid connection uses GSS in the boundary elements and GCMD for vertical reinforcements in the middle part of the walls, which aims to balance the cost, efficiency of construction and the mechanical performance. In order to investigate the behavior of this hybrid connection, cyclic test with a high axial compression ratio of 0.24 on seven full scale shear wall specimens was conducted, with the consideration of different splicing methods (hybrid, GCMD and GSS) and rows of connections (one-row and two-row). Test results indicated that all PCSWs failed by flexural-shear and their hysteretic loops were relatively plumper than the CIP reference wall. The load carrying capacity of all specimens was very close and their differences were less than 10%. The displacement ductility of the PCSWs with hybrid connections was 2.45 and 3.08, which was lower than the specimens with GSS and GCMD connections, but was still significantly higher than that of the CIP specimen (1.82). The ductility of the PCSW with one-row hybrid connections was found slightly better than that of the specimens with two-row connections. It was also revealed that specimens with hybrid connections had very similar stiffness degradation characteristics to those of the CIP specimen and showed dramatically higher energy dissipation capacity. Moreover, based on the test results, a degraded quadrilinear restoring force model was proposed.

Reversed cyclic tests on precast concrete shear walls with grouted corrugated metallic duct connections

The grouted corrugated metallic duct (GCMD) connections represent a feasible solution for precast concrete shear walls (PCSWs) thanks to their lowered construction difficulty, improved grouting reliability and reduced costs compared with the grouted steel sleeve splices (GSS). However, applications and related studies on PCSWs with GCMD are very limited, especially for their use in seismic active regions. Reversed cyclic test on six full scale shear wall specimens was conducted, considering both low and high axial compression ratios of 0.12 and 0.3. The test program includes two PCSWs with hybrid connections (GSS in the boundary elements and GCMD in the middle part of the walls), two PCSW with GCMD and two CIP reference specimens. Test results showed that all specimens failed by flexural-shear and the walls under high axial compression underwent earlier failure. The hysteretic curves of the PCSWs were found relatively wider than the CIP walls. The load carrying capacities of the PCSWs were very close to that of the CIP specimen. Under low axial compression, the PCSWs with GCMD, with hybrid connection and the CIP wall shared similar displacement ductility (4.11, 4.35 and 4.44, respectively). Under higher axial compression, the ductility of the PCSWs with GCMD (2.42) and with hybrid connections (2.36) was very close, which however was significantly higher than that of the CIP specimen (1.63). In addition, it was also revealed that precast specimens with GCMD had similar stiffness degradation characteristics to those of the PCSWs with hybrid connection and CIP specimen.

Hysteresis behavior of precast concrete composite shear walls with improved vertical connections

Precast concrete composite shear walls (PCCSWs) is a new type of precast shear wall with single- or double-layer precast panels and a cast-in-place (CIP) concrete layer (i.e., precast single wall, PSW, or precast double wall, PDW). PCCSWs could form a solid concrete structure with a shorter superstructure construction time. Therefore, these walls have become a promising precast concrete structural system for high-rise buildings worldwide. The objective of this study was to investigate the hysteresis behavior of PDWs and PSWs with improved vertical connections from the perspectives of efficiency in load transfer and simplicity in construction for applications in seismic zones. Low-reversed cyclic testing was conducted for six full-scale PCCSWs with two different axial load ratios (0.09 and 0.23). The six walls included four PDWs with two types of vertical connections (double-row spiral-confined lap connection and single-row protruding rebar lap connection) and two PSWs with a spiral-confined lap connection. The results revealed that the specimens exhibited monolithic behavior and flexural-shear failure, as expected. The difference in load capacity between the PCCSWs and CIP walls was less than 10%. All the walls had plump hysteresis loops and adequate energy dissipation performance. PDWs with the double-row spiral-confined lap connection had the highest ductility ratio (4.57 for the low axial ratio, 3.50 for the high axial ratio). The single-row protruding rebar lap connection enabled the PDWs to demonstrate relatively good ductile behavior (3.85 for the low axial ratio and 3.39 for the high axial ratio) and simple on-site construction. Although the PSWs had the lowest ductility, the ductility was comparable to that of the CIP wall with low and high axial ratios. All the specimens had a similar tendency in terms of the backbone curves and stiffness degradation. Accordingly, a trilinear degraded restoring force model was developed for different PCCSWs by regression.

Seismic behavior of square spiral-confined high-strength concrete-filled steel tube columns under high axial load ratio

Adding internal spiral reinforcement is an effective and practical approach to enhancing the ductility of square concrete-filled steel tube (CFST) columns with high-strength concrete (HSC). To investigate the seismic behavior of CFST and spiral-confined concrete-filled steel tube (SCCFST) columns with HSC under high axial load ratio, four CFST columns and four SCCFST columns with concrete strengths not less than 110 MPa were tested under combined axial and lateral loading. The test variables included the concrete compressive strength, the axial load ratio, and the lateral-loading protocol. The test results demonstrated that adding spiral reinforcement can offset the reduction of ductility caused by the increase of the axial load ratio. The ultimate drift ratios of the columns under an axial load ratio of 0.5 increased from approximately 2.0% to 3.5% after adding spiral reinforcement with a volumetric ratio of 3.13%. Increasing the concrete strength from 110 to 140 MPa essentially did not affect the deformation capacity of the columns. Due to the cyclic degradation effect, the deformation capacity of the specimen under cyclic loading was much smaller than that of the corresponding specimen under monotonic loading. The column axial shortening accumulated during cyclic lateral loading and increased exponentially when significant strength degradation started. The rotation at the column base contributed a significant portion to the total lateral displacement, indicating the necessity of considering the flexibility of the column base in structural analysis.

Experimental study on seismic behavior of precast concrete beam-column joints using UHPC-based connections

Ultra-high performance concrete (UHPC) with high bond characteristics with reinforcing bars could significantly shorten the lap splice length of rebars. UHPC-based rebar lap splice connections offer larger tolerance and simpler operation than traditional rebar connection approaches, which could ease and accelerate the on-site construction process of precast concrete structures. This paper characterizes the seismic behavior of precast beam-column joints where the longitudinal rebars of columns are connected using UHPC with a lap length of 15 times rebar diameter (15db). Full-scaled cyclic tests on two precast joints and two corresponding monolithic joints to compare were carried out keeping a high axial compression ratio (n) at 0.5. It was demonstrated that the beam-column subassemblies failed characterized by flexural failure of beam end instead of the column or joint core. The arch-like load–displacement curves and stable hysteretic behavior were still captured considering the p-delta effect. The proposed precast beam-column joints with UHPC-based connections could achieve similar bearing capacity, ductility and stiffness degradation rule to the monolithic counterparts. The degenerated four-linear restoring force model was presented and verified. Moreover, the numerical simulation was also performed, and the predicted structural behavior was in agreement with the experimental results.