Load-vertical Displacement Curves Research Articles

Axial compressive behavior of partially encased composite reactive powder concrete columns after high-temperature exposure

Replacing ordinary concrete in partially encased concrete (PEC) columns with high-strength and durability reactive powder concrete (RPC) significantly improves their axial capacity and suppresses local buckling of the steel section. To study the axial mechanical performance of partially encased composite reactive powder concrete (PEC-RPC) columns after exposure to high temperatures, axial compression tests of eight PEC-RPC column specimens were designed and conducted. Thermal response, failure modes, axial load-vertical displacement curves, and strain-axial strain curves of different specimens were observed considering the effects of link spacing, cross-sectional dimensions, constant temperature duration, and cooling methods. Results indicate: PEC-RPC columns exhibited whitening on the surface of RPC after high-temperature exposure, specimens with the largest link spacing experienced RPC peeling due to concentrated thermal stress, exacerbated by spraying water, which created a stress difference between the surface and the interior, resulting in RPC peeling. The deeper the thermocouple was embedded, the lower the measured temperature. Additionally, due to the significantly lower thermal conductivity of RPC compared to steel, the temperature at measurement points within the RPC is much lower than that at the steel web. The failure mode of PEC-RPC columns after axial loading was characterized by the crushing of RPC and local buckling of section steel. The larger the link spacing, the more prone it was to multi-layer buckling, and columns with larger cross-sectional sizes tended to exhibit shear failure. The characteristic value of mechanical performance showed higher sensitivity to cross-sectional dimensions, but relatively lower sensitivity to link spacing and constant temperature duration. As the cross-sectional dimensions increased from 150×150 mm to 250×250 mm, the peak load, residual bearing capacity, stiffness, and ductility increased by 72.51–164.86 %, 89.8–173.6 %, 61.85–151.47 %, and 13.72–31.46 %, respectively. Finally, based on partition constraint theory and superposition principle, a simplified method for calculating the axial mechanical performance of PEC-RPC columns after exposure to high temperatures was proposed.

Axial-flexural behaviours of concrete-filled square GFRP tubular columns under low temperatures

This study reported experimental investigations on the axial-flexural behaviours of concrete-filled square glass fiber-reinforced polymer (GFRP) tubular (CFSFT) columns at low temperatures. Twenty CFSFT columns under eccentric loads and two-point loading were conducted to evaluate the influences of low temperatures (T = 20 and −60 °C) and eccentricity ratios (e/r = 0.00, 0.25, 0.50, and 0.75). Failure modes, load–displacement behaviours, and load–strain behaviours at low temperatures have been reported. Test results indicated the load-vertical displacement curves of CFSFT columns under eccentric loads exhibited three different stages, i.e., linear, transition, and strain hardening or softening stage. Meanwhile, the bilinear load–deflection curves were observed for CFSFT columns under four-point bending. Based on these test results, the experimental axial load-moment (NT-MT) curves of CFSFT columns were obtained. These curves indicated that decreasing the temperature from 20 to −60 °C observably increased both the ultimate axial load (NuT) and ultimate bending moment (MuT) of CFSFT columns. However, the increment of both ultimate axial load and ultimate bending moment gradually decreased with the increasing eccentricity ratios.

Flexural Strength of Fibrous Light-Weight Self-Compacted Concrete beams

In this research, the effect of using steel fiber and polypropylene on the behavior of the lightweight self-compacting concrete (LWSCC) beams have been studied. Seven beams have been cast with different parameters and compared. Two ratios of coarse aggregate replacement with light-weight aggregate expanded clay (LECA) have been considered partially and full replacement (50% and 100%) in this study based on previous study. Also, a 1% volumetric ratio fiber reinforcement has been added to investigate its effect on the flexural performance of LWSCC. A reduction in the ultimate load capacity and stiffness have been observed for LWSCC beams compared with the control beam by about 19% and 24.8% for partial and full LECA replacement, respectively. The steel fiber enhanced the performance of LWSCC beams in terms of cracking formation, crack width, ultimate capacity and allow the beams to have more ductile behavior. The ultimate load for fibrous LWSCC has been increased by about 11% and 12% for partial and full LECA replacement compared to beams without fibers. Beams with polypropylene and steel fibers exhibit similar behavior to the beams with steel fiber only in term of load-vertical displacement curves. However, the difference in the ultimate load capacity were 4% and 5% for the partial and full LECA replacement, respectively.

Experimental Verification on Finite Element Model of Composite Columns with Concrete Filled Steel Tube Flange

In order to study mechanical performance of composite columns with concrete-filled steel tube flange subjected to the eccentric compression, the finite element model of this kind of composite columns is established by using ABAQUS finite element software. In this paper, the reasonable material constitutive and finite element modelling method are selected to carry out numerical simulation analysis of concrete-filled steel tubular composite columns and concrete-filled square steel tubular columns. The load vertical displacement curves, load lateral deflection curves and failure modes are obtained, which are in good agreement with the existing test data. The rationality of material constitutive and finite element modelling is verified, which lays a foundation for further establishing the calculation formula of eccentric compression bearing capacity of this kind of column.

Experimental investigation on the flexural behavior of pervious concrete beams reinforced with geogrids

Abstract Pervious concrete has been widely used due to the environmental and stormwater management benefits. However, its susceptibility to cracking and low flexural strength limited the widespread use for vehicular traffic pavement. This paper focuses on the flexural behavior of pervious concrete beams reinforced by geogrids with different layer number at various positions. The influences of the embedded geogrids on effective porosity, strength and cracking behaviors are studied. The load-vertical displacement curves are obtained by four-point bending tests to describe the toughness and post-cracking performance of pervious concrete beams. Meanwhile, the acoustic emission (AE) and digital image correlation (DIC) techniques are used to monitor the internal fracture characteristics, strain fields and crack propagation. The experimental results indicate that the compressive strength and flexural strength of pervious concrete can be improved owing to the embedded geogrids. Notwithstanding an increased porosity is induced, the reinforced beams demonstrate significantly superior post-crack performance. Furthermore, the embedded geogrids in pervious concrete restrain the generation and propagation of the crack, resulting in a low strain field level as well as showing a short crack length and a small crack mouth opening displacement (CMOD). Embedding the geogrids at both one-third depth and two-thirds depth of the thickness provides the optimal performance.

Behaviour of grouted stainless steel tubular X-joints with CHS chord under axial compression

An experimental investigation was conducted on empty and grouted stainless steel tubular X-joints with circular hollow section (CHS) chord member under axial compression. A total of 25 specimens including empty tubular joints, tubular joints with grouted brace members only, tubular joints with grouted chord member only and tubular joints with both grouted brace and chord members were tested. The joint strengths, failure modes, axial load-vertical displacement curves, axial load-chord deformation curves and strain distribution curves of all specimens were reported. The corresponding finite element analysis (FEA) was also performed and calibrated against the test results. Therefore, an extensive parametric study was carried out to evaluate the effects of main influential factors (β, τ, grouting and grout strength) on the behaviour of grouted stainless steel tubular X-joints with CHS chord member under axial compression. It is shown from the comparison that the ultimate strengths of empty and grouted stainless steel tubular X-joints generally increased with the increase of the β and τ values. Furthermore, the ultimate strengths of stainless steel tubular X-joints with both grouted brace and chord members generally increased with the increase of the grout strength. Whereas, the grout strength has little influence on the ultimate strengths of stainless steel tubular X-joints with grouted chord member only. On the other hand, the joint strengths obtained from the tests and parametric study were compared with the design strengths calculated using the current design rules. It is shown from the comparison that the current design rules are generally unconservative for empty and grouted stainless steel tubular X-joints with CHS chord member under axial compression. Therefore, the new design equations were proposed in this study, which were verified to be more accurate.

Investigation of grouted stainless steel SHS tubular X- and T-joints subjected to axial compression

An experimental investigation was conducted on empty and grouted stainless steel square hollow section (SHS) tubular X- and T-joints subjected to axial compression. A total of 24 specimens including empty tubular joints, tubular joints with grouted brace members only, tubular joints with grouted chord member only and tubular joints with both grouted brace and chord members were tested. The joint strengths, failure modes, axial load-vertical displacement curves, axial load-chord deformation curves and strain distribution curves of all specimens were reported. The corresponding finite element analysis (FEA) was also performed and calibrated against the test results. Therefore, an extensive parametric study was carried out to evaluate the effects of main influential factors (β, τ, grouting and grout strength) on the behaviour of grouted stainless steel SHS tubular X- and T-joints subjected to axial compression. It is shown from the comparison that the ultimate strengths of empty and grouted stainless steel SHS tubular X- and T-joints generally increased with the increase of the β and τ values. The enhancement of joint strengths obtained from grouting both brace and chord members is much greater than that obtained from grouting chord member only. In addition, the ultimate strengths of stainless steel SHS tubular X- and T-joints with both grouted brace and chord members generally increased with the increase of the grout strength. Whereas, the grout strength has little influence on the ultimate strengths of stainless steel SHS tubular X-joints with grouted chord member only. On the other hand, the joint strengths obtained from the tests and parametric study were compared with the design strengths calculated using the current design rules. It is shown from the comparison that the current design rules are generally conservative for the design of empty stainless steel SHS tubular X- and T-joints subjected to axial compression, but unconservative for the design of grouted stainless steel SHS tubular X- and T-joints subjected to axial compression. Therefore, the new design equations were proposed in this study, which were verified to be more accurate.

Flexural behaviour of concrete-filled CHS X-joints with curved chord under out-of-plane bending

This paper presents experimental and numerical investigations on empty and concrete-filled circular hollow section (CHS) X-joints with curved chord under out-of-plane bending. A total of 16 specimens were fabricated by hot-rolled bending the chord members into curvature with three different radii to apply out-of-plane bending to the brace members, in which 6 specimens were tested with empty curved chord, 6 specimens were tested with concrete filled in the curved chord only, and 4 traditional empty and concrete-filled CHS X-joints with straight chord were also tested for comparison. The typical failure modes, axial load-vertical displacement curves, bending moment-chord deformation curves, bending moment-rotation curves and strain distribution curves of all specimens are reported. The effects of curvature radius of chord member and concrete filled in the chord member on the joint strength and behaviour under out-of-plane bending were evaluated. It is shown from the comparison that the ultimate strengths of the CHS X-joints with curvature radius of chord less than 12d0 under out-of-plane bending are closer to those of the traditional CHS X-joints with straight chord with the increase of the curvature radius of chord member. Whereas, the ultimate strengths of the CHS X-joints with curvature radius of chord less than 12d0 under out-of-plane bending are generally similar to those of the traditional CHS X-joints with straight chord. Furthermore, the out-of-plane flexural behaviour of CHS X-joints are improved with the increase of the β ratio. Whereas, filling the concrete in the chord member cannot enhance the ultimate strengths of CHS X-joints under out-of-plane bending. The joint strengths obtained from the experimental investigation are compared with the design strengths calculated using the current design rules for traditional CHS X-joints with straight chord under out-of-plane bending, which were demonstrated to be quite conservative. In addition, the corresponding finite element analysis was also performed and calibrated against the test results. The design equations are proposed based on the test and numerical results for empty and concrete-filled CHS X-joints with curved chord under out-of-plane bending, which were verified to be more accurate.

Tests of CHS T-joints with convex chord under axial compression

An experimental investigation was conducted on circular hollow section (CHS) T-joints with convex hollow and concrete-filled steel tube (CFST) chord under axial compression. A total of 16 specimens was fabricated by hot-rolled bending the chord members into curvature with three different radii to apply axial compression force to the brace members, in which 6 specimens were tested with convex hollow chord, 6 specimens were tested with convex CFST chord, and 4 traditional CHS T-joints with straight hollow and CFST chord were also tested for comparison. The joint strengths, failure modes, axial load-vertical displacement curves, axial load-chord deformation curves and strain distribution curves of all specimens are reported. It is shown from the comparison that the ultimate strengths of the CHS T-joints with convex chord are generally larger than those of the traditional CHS T-joints with straight chord. Furthermore, the ultimate strengths of traditional CHS T-joints with straight chord are significantly enhanced by filling the concrete in the chord member only. Whereas, the enhancement of the ultimate strengths of CHS T-joints with convex chord by filling the concrete in the chord member only is quite small.

Tests of SHS brace-H-shaped chord X-joints under in-plane bending

This paper presented an experimental and numerical investigation on the square hollow section (SHS) brace-H-shaped chord X-joints under in-plane bending. A total of 8 specimens were tested to study the static behavior of the unstiffened and stiffened X-joints under in-plane bending. The test procedure, failure modes, load-vertical displacement curves, moment-rotation curves, load-deformation curves and strain intensity distribution curves were all reported. For the joints with 90° stiffeners, the bending ultimate capacity increased. However, for the joints with 45° stiffeners, the bending ultimate capacity decreased. Effect of external stiffener on initial stiffness of joints was unobvious. With the increment of β, the initial stiffness of joints under in-plane bending increased. The local deformation of the brace members of X-joints with big β was smaller than that of joints with small β. 90°stiffeners could delay the plasticity process of the joints with big β. 45° stiffeners could not delay the plasticity process of the joints with big β. The test results were compared with the design strengths calculated using the current Eurocode 3. It is shown from the comparison that the current Eurocode3 was generally conservative for the design of the SHS brace-H-shaped chord X-joints under in-plane bending. The FEA model of joints was validated by comparing test result with numerical result in the term of failure modes, load-vertical displacement curves and ultimate capacity.The effects of ratio of side length of brace to chord flange width β, ratio of chord flange width to double thickness of chord flange γ and ratio of brace to chord thickness τ on ultimate capacity of the joints were also numerically studied in parametric analysis. New design equations of ultimate capacity of SHS brace-H-shaped chord unstiffened X-joints under in-plane bending were proposed in this study which was proved to be more accurate and reliable.

Axial compression physical testing of traditional and bird beak SHS T-joints

The static tests of nine traditional and bird beak square hollow structure (SHS) T-joints with different s values and connection types under axial compression at brace end were carried out. Experimental test schemes, failure modes of specimens, jack load-vertical displacement curves, jack load-deformation of chord and strain intensity distribution curves of joints were presented. The effects of s and connection types on axial compression property of joints were studied. The results show that the ultimate axial compression capacity of common bird beak SHS T-joints and diamond bird beak SHS T-joints is larger than that of traditional SHS T-joint specimens with big values of s. The ultimate axial compression capacity of diamond bird beak SHS T-joints is larger than that of common bird beak SHS T-joints. As s increases, the increase of the ultimate axial compression capacity of diamond bird beak SHS T-joints over that of common bird beak joints grows. The ultimate axial compression capacity and the initial axial stiffness of all kinds of joints increase as s increases, and the initial axial stiffness of the diamond bird beak SHS T-joints is the largest. The ductilities of common bird beak and diamond bird beak SHS T-joints increase as s increases, but the ductility of the traditional SHS T-joints decreases as s increases.

Behaviour of bird-beak square hollow section X-joints under out-of-plane bending

An experimental investigation was conducted on bird-beak square hollow section (SHS) X-joints under out-of-plane bending. A total of nine specimens including traditional SHS X-joints, square bird-beak SHS X-joints and diamond bird-beak SHS X-joints were tested. The test results of joint strengths, failure modes, load-vertical displacement curves, bending moment-local deformation curves, bending moment-rotation curves, and strain distribution curves of all specimens were reported. The corresponding finite element analysis (FEA) was also performed and calibrated against the test results. Therefore, an extensive parametric study was carried out to evaluate the effects of main geometric parameters (β, τ and 2γ) on the behaviour of bird-beak SHS X-joints under out-of-plane bending. It was shown from the comparison that the ultimate strengths and initial stiffness of all specimens under out-of-plane bending significantly increased with the increase of the β ratio. The ultimate strengths of bird-beak SHS X-joints under out-of-plane bending are generally much larger than those of traditional SHS X-joints. Furthermore, the ultimate strengths of diamond bird-beak SHS X-joints under out-of-plane bending are always larger than those of square bird-beak SHS X-joints. The joint strengths obtained from the experimental investigation were compared with the design strengths calculated using the current Eurocode 3 and IIW Specification for traditional SHS X-joints under out-of-plane bending, which were demonstrated to be quite conservative. In addition, the design equations are proposed for bird-beak SHS X-joints under out-of-plane bending, which were shown to be accurate and reliable.

Bearing Capacity Analysis on Improved Slotted End Plate Connections

Full-scale of U-type and grooved-type slotted end plate (SEP) connections are tested to determine their failure modes and damage mechanisms under ultimate loading. Simulate on mechanical behaviors of U-type and grooved-type SEP connections under compression using finite element software ANSYS based on the experimental research. Obtain load-vertical displacement curves of the SEP connections, and compare with the experimental results to determine the validity of the model. On this basis, this paper provide the improved SEP connections, and contrast with the U-type and grooved-type SEP connections. The results indicate that finite element results are in good agreement with experimental data. Difference of the ultimate load between the test specimen and finite element model is less than 10%. The finite element can simulate mechanical behaviors of the SEP connections better. The ultimate bearing capacity of the UC-type SEP connected joints is significantly higher than the U-type and grooved-type, which shows the improved SEP Connections is reasonable and effective. SEP is the main factor of the U-type and grooved-type SEP Connections’ ultimate load, tube is controlling factor of the UC-type SEP connected joints.