Experimental study on axial compression performance of mortise-and-tenon precast concrete beam–column joints

A reliability analysis of the axial compressive load bearing capacity of postfire reinforced concrete (RC) columns strengthened with carbon fiber reinforced polymer (CFRP) sheets was presented. A 3D finite element (FE) model was built for heat transfer analysis using software ABAQUS. Based on the temperature distribution obtained from the FE analysis, the residual axial compressive load bearing capacity of RC columns was worked out using the section method. Formulas for calculating the residual axial compressive load bearing capacity of the columns after fire exposure and the axial compressive load bearing capacity of postfire columns retrofitted with CFRP sheets were developed. Then the Monte Carlo method was used to analyze the reliability of the axial compressive load bearing capacity of the RC columns retrofitted with CFRP sheets using a code developed in MATLAB. The effects of fire exposure time, load ratio, number of CFRP layers, concrete cover thickness, and longitudinal reinforcement ratio on the reliability of the axial compressive load bearing capacity of the columns after fire were investigated. The results show that within 60 minutes of fire exposure time, the reliability index of the RC columns after retrofitting with two layers of CFRPs can meet the requirements of Chinese code GB 50068 (GB 2001) for safety level II. This method is effective and accurate for the reliability analysis of the axial load bearing capacity of postfire reinforced concrete columns retrofitted with CFRP.

Since its introduction in 1973, the Davisson Offset Limit has been widely used in the United States for interpretation of axial compressive load tests on pile foundations and is one of three methods explicitly accepted by the 2006 International Building Code. An examination of the fundamental assumptions of the DOL shows that its application to cast-in-place piles lacks scientific basis and leads to over conservatism. Interestingly, these are the same reasons given by Davisson for its development. The results of the examination indicate that there are notable fallacies in the Davisson Offset Limit, including the assumptions that: (1) the cast-in-place pile behaves as a “fixed-base, free-standing column.”, (2) an elastic line is a dependable reference line for interpretation of load tests on cast-in-place piles, and; (3) an offset of 3.8 mm + D (inches)/120 from the elastic line represents the movement necessary to mobilize toe resistance of cast-in-place piles. Considering these results, the authors present suggestions ranging from modifications to the Davison Offset Limit that recognizes the greater movement required to mobilize the toe resistance to codification of a more rational criterion better suited to interpret the axial compressive capacity of cast-inplace piles. INTRODUCTION The 2006 International Building Code explicitly accepts three interpretive methods for axial compressive load tests on piles. These three interpretative methods (by the names they are used in common vernacular): (1) Davisson Offset Limit (Davisson, 1972); (2) Brinch Hansen 90% Criterion (Brinch Hansen, 1963), and; (3) Butler-Hoy Criterion (Butler and Hoy, 1977). Generally speaking, the Davisson Offset Limit (DOL) is frequently used in the United States because it provides the lowest estimation of axial compressive capacity of the aforementioned methods. Also, it is most likely to provide an ultimate axial compressive pile capacity from the actual load-deflection curve. That is, the Brinch Hanson 90% Criterion and the Butler-Hoy Criterion often require extrapolation to extend the load-deflection curve in order to establish an ultimate axial compressive capacity. In the absence of established guidelines for extrapolation, there is a reluctance, and even opposition, to the extrapolation of load test results. 568 DEEP FOUNDATIONS

Experimental study on axial compression performance of unbonded prestressed mortise-tenon precast concrete mid joint

Axial strength and ductility of square composite columns with two interlocking spirals

In this study, the mechanical performance of multicavity concrete‐filled steel tube (CFST) shear wall under axial compressive loading is investigated through experimental, numerical, and theoretical methodologies. Further, ultrasonic testing is used to assess the accumulated damage in the core concrete. Two specimens are designed for axial compression test to study the effect of concrete strength and steel ratio on the mechanical behavior of multicavity CFST shear wall. Furthermore, a three‐dimensional (3D) finite element model is established for parametric studies to probe into compound effect between multicavity steel tube and core concrete. Based on finite element simulation and limit equilibrium theory, a practical formula is proposed for calculating the axial compressive bearing capacity of the multicavity CFST shear wall, and the corresponding calculation results are found to be in good agreement with the experimental results. This indicates that the proposed formula can serve as a useful reference for engineering applications. In addition, the ultrasonic testing results revealed that the damage process of core concrete under axial load can be divided into three stages: extension of initial cracks (elastic stage), compaction due to hooping effect (elastic‐plastic stage), and overall failure of the concrete (failure stage).

This study examines the axial compression performance of unbonded prestressed mortise–tenon beam–column joints (MTPC). The MTPC joint employs a mortise–tenon configuration, achieving tight compression through unbonded prestressed steel strands at the column's center, enhancing prefabrication efficiency. Three axial compression test models were fabricated and subjected to axial monotonic loading, with experimental phenomena and results analyzed. The results show the optimized MTPC joint achieves approximately 90% of the column‐end axial capacity, while MTPC joints reinforced with ultra‐high‐performance concrete (UHPC) surpass the column‐end capacity, fulfilling the “strong joints, weak components” design principle. Minor gaps during assembly require axial pressure for tight component contact, but the assembled joint demonstrates excellent integrity, stable axial stiffness, and effective load transfer. A calculation method for the axial load‐bearing capacity of MTPC joints is proposed, along with a finite element model. Comparison with experimental results validates the model's accuracy. Theoretical calculations, experimental data, and finite element analysis collectively confirm the proposed method effectively predicts the axial compression capacity and mechanical behavior of MTPC joints under axial loading. This research highlights the MTPC joint's potential for enhancing construction efficiency and structural performance in prefabricated systems.

Fiber‐reinforced polymer (FRP) rebars have become an attractive alternative for replacing steel reinforcement due to their superior corrosion resistance. Columns reinforced with GFRP rebars can fail in a brittle manner than those reinforced with steel rebars. Adding discrete fibers in GFRP‐reinforced concrete (RC) columns can improve its ductility by bridging the cracks formed in concrete. Both steel and synthetic discrete fibers can be combined to form hybrid fiber‐reinforced concrete (HFRC) which synergizes the advantages of both fiber types. An analytical approach is presented here to estimate the axial compression (P) and bending moment (M) interaction behavior of FRC GFRP columns. Moment‐curvature analysis using suitable constitutive relations for concrete and GFRP bars under compression and tension is adopted. Bending moment capacity at different axial compression loads is established. Later, P–M interaction curves for square RC columns with GFRP rebars and discrete fibers are obtained and validated with test results. After that, a parametric study is carried out to understand the effect of concrete strength, amount of reinforcement, and different fiber dosages for GFRP RC columns. Results show that adding fibers can improve the bending and compression capacities at all combinations of axial and bending loads. The axial compression and bending capacity of the steel RC and GFRP columns with equal reinforcement ratios showed that GFRP HFRC had higher capacity than steel RC column sections under combined axial and bending loads.

Cold-formed steel framing walls with infilled lightweight FGD gypsum Part II: Axial compression tests

The axial compressive experiments were carried out on 21 welded composite T-shaped concrete-filled steel tubular columns, and 395 finite element models were established for parameter calculation. The calculating formula of axial compressive bearing capacity of welded composite T-shaped concrete-filled steel tubular columns is established. The results show that three typical failure modes were found: middle buckling, end local buckling, and integral bending. When the slenderness ratio λ exceeds the elastic instability limit λp, the axial stress of steel is lower than yield strength fy, and the axial stress of core concrete is lower than axial compressive strength fc. Increasing the thickness of steel has a more obvious effect on increasing the axial compressive bearing capacity of specimen. The theoretical calculating formula can effectively predict the axial compressive bearing capacity, and the theoretical calculation is partial to safety. The average ratio of axial compressive bearing capacity of the theoretical calculation to the experimental is 0.909, and the standard deviation is 0.075. The average ratio of axial compressive bearing capacity of the finite element calculation to the experimental is 0.957, and the standard deviation is 0.045. The average ratio of axial compressive bearing capacity of the theoretical calculation to the finite element calculation is 0.951, and the standard deviation is 0.039.

This study suggests a joint design using an X-brace bar to identify the stability and structural performance of a precast concrete (PC) beam-column joint design, which may cause problems when used in a segmented PC beam system for a long-span structure. For this, an experimental PC beam-column model at half scale was designed and veri­fied for applicability of X-braced bars in a panel zone. While previous studies suggested the development of a long-span structural system using precast concrete (PC) and described the problems with PC beam-column joints, this study proposes a solution to improve the structural stability and performance of a PC beam-column joint design and conducts analytical verification.

Performance of stirrup-confined concrete-filled steel tubular stub columns under axial loading: A further investigation

To investigate the axial compressive performance of the recycled aggregate concrete (RAC) filled glass fiber reinforced polymer (GFRP) tube and profile steel composite columns, static loading tests were carried out on 18 specimens under axial loads in this study, including 7 RAC filled GFRP tube columns and 11 RAC filled GFRP tube-profile steel composite columns. The design parameters include recycled coarse aggregate (RCA) replacement percentage, profile steel ratio, slenderness ratio and RAC strength. The failure process, failure modes, axial stress-strain curves, strain development and axial bearing capacity of all specimens were mainly analyzed in detail. The experimental results show that the GFRP tube had strong restraint ability to RAC material and the profile steel could improve the axial compressive performance of the columns. The failure modes of the columns can be summarized as follow: the profile steel in the composite columns yielded first, then the internal RAC material was crushed, and finally the fiberglass of the external GFRP tube was seriously torn, resulting in the final failure of columns. The axial bearing capacity of the columns decreased with the increase of RCA replacement percentage and the maximum decreasing amplitude was 11.10%. In addition, the slenderness ratio had an adverse effect on the axial bearing capacity of the columns. However, the strength of the RAC material could effectively improve the axial bearing capacity of the columns, but their deformability decreased. In addition, the increasing profile steel ratio contributed to the axial compressive capacity of the composite columns. Based on the above analysis, a formula for calculating the bearing capacity of composite columns under axial compression load is proposed, and the adverse effects of slenderness ratio and RCA replacement percentage are considered.

Test on compressive performance of hollow concrete filled circular steel tube connected by thread through inner lining tube

The construction industry has been a significant contributor to global carbon emissions. Fortunately, it is well known that precast concrete structures possess the benefit of reducing carbon emission, of which the beam–column joint plays a crucial role in resisting severe loads. Nowadays, the cast-in-place joint is mostly adopted for beam–column joint The authors declare no conflict of interests of precast concrete structures, and the building industrialization degree is insufficient. In light of this, a novel precast concrete beam–column joint using the mortise–tenon (MT) connection is proposed inspired by traditional timber structures, and the contrastive analysis of mechanical behaviors of this joint and the same-sized cast-in-place joint is conducted by the finite element method. The results indicate that the proposed MT joint has a better mechanical behavior by comparing with the corresponding cast-in-place joint as the beam–column joint. Meanwhile, the MT connection mode has the characteristics of standardized construction, in line with the concept of sustainable development, which can greatly save the construction period. This research demonstrates the feasibility of MT joints in traditional timber structures as beam–column joints in precast concrete structures, and the application of MT joints may be promoted if the size and shape of that are further optimized. Furthermore, this in turn helps research and innovation of precast building construction technology and promotes the sustainable development of the construction industry in the direction of energy conservation and environmental protection.

Experimental evaluation of axial compression performance of precast panels from bamboo-reinforced concrete