Code For Design Of Concrete Structures Research Articles

Experimental study of the bond behavior of 400MPa grade hot-rolled ribbed steel bars in steel fibre reinforced concrete

Present studies show that steel fibres can improve the bond of steel bar in steel fibre reinforced concrete (SFRC) with a correlation to the fibre factor and the fibre distribution uniformity. As a foundation of high-flowability SFRC working together with 400 MPa grade hot-rolled ribbed (HRB400) steel bar in reinforced structures, the bond between them was evaluated through a series of pull-out testing on 48 specimens with a central arranged steel bar. The bond behaviours of steel bar were estimated with a constant bond length of 5d (d is the diameter of steel bar) embedded in high-flowability SFRC, the main research parameters included the ingot mill steel fibres with a fibre volume fraction varied from 0.8 to 2.0%, the strength grade C40 and C50 of SFRC or referenced conventional concrete, and the diameter of steel bars varied from 14 to 20 mm. Results showed that the high-flowability SFRC compacted with a slight vibration is beneficial to improve the bond failure pattern since steel fibres effectively eliminate the crack appeared on the SFRC blocks during the pulling out of steel bar, leading to all specimens failed with the steel bar pull out of SFRC blocks. The bond strength was dominant by the SFRC strength, and obviously strengthened with the increase of fibre volume fraction, while the peak-slip was slightly influenced by the diameter of steel bar. By conducting analyses of test data, equations for calculating the bond strength and the peak-slip are proposed accounting for the effect of steel fibres. Then the predicting method for the anchorage length is suggested linking with different design codes for concrete structures. Compared with test results of this study, a little shorter anchorage length of steel bar in SFRC is obtained from the specification of Chinese code JGJ/T46, which should be noticed to ensure a rational anchorage of ribbed steel bar in SFRC with ingot mill steel fibres.

Study on Eccentric Compressive Behavior of Concrete Columns Reinforced with NPR735 High-Strength Steel Bars

In this paper, eccentric compressive tests and theoretical studies of grade 735 MPa reinforced concrete columns were conducted. The eccentric distance and strength of the longitudinal reinforcement were used as experimental parameters to investigate the bearing capacity, failure mode, and strength of eccentric compressive behavior of NPR735 high-strength steel bars. When the load eccentricity of the reinforced concrete columns was small or longitudinal, the reinforcement ratio was large, and small eccentricity failure occurred. The results were similar to the failure mode of ordinary concrete columns with traditional steel bars. When the load eccentricity decreased, the bearing capacity increased, but the deflection and ductility of the specimen decreased. When the strength of the longitudinal reinforcement increased, the bearing capacity of the specimen increased slightly. Finally, according to current design methods in the concrete structure design code, the bearing capacity of the eccentric compressive column was obtained, and the calculated results were compared with the experimental results to verify the applicability of the concrete structure design code GB50010-2010 to concrete columns with grade 735 MPa reinforcement.

Effect of stress-strain models and sectional analysis methods on the axial-flexural interactions of discontinuously FRP strengthened square RC columns

This study analytically investigated the axial-flexural (P-M) interactions of quare reinforced concrete (RC) columns discontinuously strengthened swith fibre reinforced polymers (FRP). Six FRP confined concrete stress-strain models and two sectional analysis methods were used to develop the analytical P-M interactions of discontinuously FRP strengthened square RC columns. The developed analytical P-M interactions were validated against experimental data available in the literature. It was found that the selection of the stress-strain models had a substantial effect on the analytical P-M interactions, while the influence of the sectional analysis methods heavily depended on the selected stress-strain models. It was also found that the three available design codes for concrete structures externally strengthened with FRP yielded different analytical P-M interactions of discontinuously FRP strengthened square RC columns. A parametric analysis was undertaken and found that the corner radius and confinement ratio significantly affected the P-M interactions of discontinuously FRP strengthened square RC columns. Also, discontinuously FRP strengthened square RC columns with a higher number of FRP layers and smaller corner radius obtained lower flexural and axial strengths than their counterparts with a lower number of CFRP layers and higher corner radius.

Finite Element Analysis of Punching Shear of Reinforced Concrete Slab–Column Connections with Shear Reinforcement

Shear reinforcement is one of the common measures used to strengthen slab–column connections. It can make the joint’s load capacity increase. However, when the connection is subjected to an unbalanced bending moment, the reduction effect of the shear reinforcement on the bending moment is worth investigating. Nonlinear finite element analysis was performed on reinforced concrete slabs with shear reinforcement for various moment-to-shear (M/V) ratios. The effects of the number and diameter of shear reinforcement and different loading methods on the slab were investigated, as along with a correction to the ACI-318 and China Concrete Structure Design code GB50010 formula for the moment transfer coefficient. The 3D finite element modeling was performed using appropriate element types and a constitutive model for concrete. The concrete damage plasticity model parameters were calibrated using the experimental results of a specimen. The amount of shear reinforcement had a certain contribution to the strength of the slab, but the diameter of the shear reinforcement had little effect. The plate’s bearing capacity decreased as the M/V increased. The corrected moment transfer coefficient formula demonstrates that M/V is positively correlated with the coefficient and that the calculated values specified in ACI-318 and GB50010 are overly conservative.

Investigation on Hysteretic Behavior of Embedded PVC Pipe Confined Reinforced High Strength Concrete Columns.

To study the seismic performance of embedded polyvinyl chloride (PVC) pipe confined reinforced high-strength concrete (PVC-RHC) columns, five specimens are designed for cyclic loading test, which include three PVC-RHC column specimens, an embedded circle steel tube confined reinforced high-strength concrete (CST-RHC) column specimen, and a reinforced high-strength concrete (RHC) column specimen. The failure mechanism and morphology are revealed by experiments. The influences of PVC pipe diameter, axial compression ratio, and concrete strength on seismic performance indexes are analyzed. The research results indicate thhe following: all specimens displayed shear baroclinic failure. Compared with RHC specimens, the hysteretic curves of the PVC-RHC specimen and CST-RHC specimen were fuller; furthermore, their energy dissipation capacity, deformation, and ductility were more beneficial. With the increase of the diameter–length ratio and axial pressure, the energy dissipation capacity and deformation capacity of PVC-RHC specimens decreased. The shear bearing capacity of the PVC-RHC specimen calculated with “concrete structure design code” (GB 50010-2010) was smaller than the test results by 25%, showing an excessive safety margin. Thus, according to the failure mechanism of the PVC-RHC specimen, a new calculation formula of shear bearing capacity is deduced, which is in good agreement with the experimental results.

Shear Capacity of Open Sandwich Steel Plate‐Concrete Composite Slab: Experimental and Analytical Studies

Considering that the fixed crack model by default of the general finite element software was unable to simulate the shear softening behavior of concrete in the actual situation, a rotational crack model based on the modified compression field theory developed by UMAT (user material) of ABAQUS software was proposed and applied to the nonlinear analysis, and a numerical simulated model for the steel‐concrete composite slab was built for shear analysis. Experimental studies and numerical analyses were used to investigate the shear load‐carrying capacity, deformation, and crack development in steel plate‐concrete composite slab, as well as the effects of the shear span ratio and shear stud spacing on the shear performance and the contribution of the steel plate and the concrete to the shear performance. Shear capacity tests were conducted on three open sandwich steel plate‐concrete composite slabs and one plain concrete slab without a steel plate. The results indicated that the shear‐compression failure mode occurred primarily in the steel plate‐concrete composite slab and that the steel plate sustained more than 50% of the total shear force. Because of the combination effect of steel plate, the actual shear force sustained by the concrete in the composite slab was 1.27 to 2.22 times greater than that of the calculated value through the Chinese Design Code for Concrete Structures (GB 50010‐2010). Furthermore, the shear capacity of the specimen increases by 37% as the shear stud spacing decreases from 250 mm to 150 mm. By comparing the shear capacity, the overall process of load deformation development, and the failure mode, it was shown that the simulation results corresponded with the experimental results. Furthermore, the numerical simulation model was applied to analyze the influence of some factors on composite slab, and a formula of shear bearing capacity of slab was obtained. The results of the formula agreed with the test result, which could provide references to the design and application of steel plate‐concrete composite slab.

Minimum torsional reinforcement ratio for reinforced concrete members with steel fibers

The current design codes for concrete structures suggest the minimum torsional reinforcement ratio to induce minimum ductile failure after cracking in reinforced concrete (RC) members subjected to torsional moment. However, as the member strengths are quite often lower than the torsional cracking moment strengths even when satisfying minimum torsional reinforcement ratio specified in the current codes, it may not serve the original purpose of preventing brittle failure immediately after cracking. In this study, a rational equation is thus presented for calculating the minimum torsional reinforcement ratio that could provide a sufficient margin of safety in design. The minimum fiber factor to be applied in steel fiber reinforced concrete (SFRC) members is also proposed. The proposed model was found to reflect the effects of torsional cracking strength, longitudinal and transverse reinforcement ratio, and the presence of torsional reinforcement in concrete members. It was also found that as the reserved strength included in the proposed equation is determined based on the test results of the RC members, it contains an appropriate factor of safety for the RC members. In addition, it was confirmed that the minimum fiber factor is conservative compared with the collected test results of the SFRC specimens.

Effect of Global Warming on Chloride Ion Erosion Risks for Offshore RC Bridges in China

Chloride ion penetration, which leads to corrosion of steel reinforcement, is the leading cause of offshore reinforced concrete bridge deterioration. Global warming would accelerate the process of chloride ion penetration and then structural degradation. In China, durability design code for concrete structures has been issued in 2008, and some thresholds of design parameters have been specified to mitigate corrosion in concrete bridge. However, influence of global warming on structure durability was not considered in the issued code. This would overestimate the durability of concrete structures. In this paper, a reliability based method was adopted to evaluate the influence of climate change on the durability of offshore RC bridges considering the acceleration of chloride ion penetration caused by temperature rise. Two climate change scenarios according to IPCC report were considered to define the global warming. A baseline scenario, in which the mean average temperature equals to that of the year 2000, were defined. It is found that the amount of chloride ion on the surface of reinforcing steel bar in the global warming scenarios are 6%-15% higher than that of structure in the baseline scenario. Meanwhile, the probability of corrosion initiation and corrosion damage increased also. In 2100, structures in environmental categories III-C and III-F, designed according to Chinese codes, can no longer adapt the impact of climate change on structure. Comparison of reliability of improved and pre-improved structure was conducted to verify the effectiveness of the proposed improvement measures.

Stability Analysis of Wall Structure which its Depth is over Thousand m

According to the monitoring result of wall structure which its depth is over thousand, analyzed the strain of inner and outer edges of concrete and inner steel; Neglect construction factors, by comparing the strain of inner concrete and inner steel, it shows that their deformation is consistently; Using the average strain of inner and outer edges of concrete to check strength adopting method of concrete structure design code, shows that they can meet the requirement.

Research on Flexural Stiffness Reduction Factor of Reinforced Concrete Column with Equiaxial + Shaped Section

The reduced stiffness method had been adopted to evaluate the material nonlinearity characteristics of reinforced concrete structures in compliance with concrete structure standards of the United States, New Zealand and Canada. Concrete structure design code in China also accepts the reduced stiffness method as a supplement of the second-order effects. However, the concrete structure with specially shaped columns code of China still use amplified coefficients of eccentricity to consider nonlinearity characteristics of reinforced concrete structure with special shaped columns. Based on the numerical integral method, a flexural stiffness reduction factor is proposed to consider characteristics of material nonlinearity and geometrical nonlinearity of reinforced concrete columns with equiaxial + shaped section

Basic Mechanical Properties of Concrete with Machine-Made Sand and Recycled Coarse Aggregate

Experimental study was carried out on the concrete mixed with machine-made sand and recycled coarse aggregate (MSRAC), three strength grades of concrete were designed by changing the water to cement ratio as 0.36, 0.45 and 0.55, while the sand ratio varied in a range of 32%~38%, 32%~42% and 38%~44% successively. The workability and the mechanical properties such as compressive and splitting tensile strengths and elastic modulus of MSRAC were tested. The results show that although the mechanical properties of MSRAC were influenced by sand ratio, they were still controlled by the water to cement ratio. The ratio of axial compressive strength to cubic compressive strength and the elastic modulus of MSRAC basically satisfy the specifications of the current design code for concrete structures. It should be noticed that the tensile strength of MSRAC is lower than current specification, and tends to reduce with the increase of water to cement ratio.

Study on Flexural Stiffness Reduction Factor of Reinforced Concrete Column with Equiaxial T Shaped Section

The reduced stiffness method had been adopted to evaluate the material nonlinearity characteristics of reinforced concrete structures to be in compliance with concrete structure standards of the United States, New Zealand and Canada. Concrete structure design code in China also accepts the reduced stiffness method as a supplementary method of considering the second-order effects problem. However, the concrete structure with specially shaped columns code of China still use amplified coefficients of eccentricity to consider nonlinearity characteristics of reinforced concrete structure with special shaped columns. Based on the numerical integral method, a flexural stiffness reduction factor is proposed to consider characteristics of material nonlinearity and geometrical nonlinearity of reinforced concrete columns with equiaxial T shaped section.

Unified Design of Tensile-Compression Prestressed Concrete Structure

Structural characteristics of tensile-compression prestressed concrete are introduced briefly in this paper. Firstly, with current concrete structure design code（GB50010）, requirements for materials used in tensile-compression prestressed concrete structure are put forward; and for prepressing stress steel pipe, strength value and basic types for structure design are determined. Secondly the calculation method of prestress loss is given during each work stage of tensile-compression prestressed concrete; and the basic measures of cracking control are concluded. Thirdly, bearing capacity formula of tensile-compression prestressed concrete structure and stress checking formula of menbers in construction stage are provided. Finally structure design of tensile-compression prestressed concrete is unified

Quasi-Static Test of Reinforced Concrete Shear Wall with Low Concrete Strength and Reinforcement Ratio

A large number of reinforced concrete (RC) buildings constructed in the 1970s, whose main structural form is fish-bone shear wall, are still used in Qiansanmen area of Beijing. Due to the economical and technical limitation at the time, both the concrete strength and reinforcement ratio are far from satisfying the requirements given in the current seismic design code for concrete structures. In order to investigate the seismic performances of the wall with the low concrete strength and reinforcement ratio, four RC shear wall specimens were constructed and tested. Quasi-static tests considering large axial compression ratio were carried out, and the stiffness, the strength and the energy dissipation capacity of the RC shear walls are investigated. Test results suggest that the wall with low concrete strength and reinforcement ratio has low strength and poor deformation capacity, indicating the necessity of strengthening.

Experimental Study on Flexural Behavior of Recycled Coarse Aggregate Concrete Beam

In order to investigate flexural behavior of simply-supported beam using recycled coarse aggregate concrete, the difference of the component normal section stress distortion performance and failure characteristic between the recycled concrete beam and the normal concrete beam is researched. The approaches of testing the flexural behavior of 6 recycled course aggregate beams with the same section size, different replacement ratio of recycled coarse aggregate (0%, 50%, 70% and 100%) and different percentage reinforcement (0.68%, 0.89% and 1.13%). Based on the experimental the following conclusions are draw. There are also 4 phases of elasticity, cracking, yield and ultimate during the stress course of recycled concrete beam component normal section stress; the average strain measured on cross-section obliges to the plane section assumption; the characteristics of stress distortion and destruction of recycled concrete beam are basically the same as those of the normal concrete beam. Under same conditions, the cracking moment and the ultimate flexural carrying capability of recycled concrete beam is almost the same as those of normal concrete beam. The deformation of recycled concrete beam is larger than concrete beam. The conclusion of the paper is that it is still feasible to calculate the ultimate bending moment, cracking moment, and the biggest crack width of recycled concrete beam according to the formula in China Concrete Structure Design Code, but the deflection formula needs to be adjusted.

Problems with Hu-Duan Boundary Effect Model and Its Comparison to Size-Shape Effect Law for Quasi-Brittle Fracture

Recent disagreements on the mathematical modeling of fracture and size effect in concrete and other quasi-brittle materials are obstacles to improvements in design practice, and especially in design codes for concrete structures. In an attempt to overcome this impediment to progress, this paper compares the Hu-Duan boundary effect model BEM expounded since 2000 to the size-shape effect law SEL proposed at Northwestern University in 1984 and extended to the geometry or shape effects in 1990. It is found that within a rather limited part of the range of sizes and shapes, the fracture energy values identified by BEM and SEL from the test data on maximum loads are nearly the same. But in other parts of the range the BEM is either inferior or inapplicable. The material tensile strength values identified by BEM have a much larger error than those obtained from the SEL after calibration by the cohesive crack model. From the theoretical viewpoint, several hypotheses of BEM are shown to be unrealistic. DOI: 10.1061/ASCEEM.1943-7889.89 CE Database subject headings: Cracking; Concrete; Structural failures; Data analysis; Size effect. Author keywords: Fracture scaling; Fracture energy; Concrete; Asymptotics of fracture; Cohesive cracks; Failure of structures; Evalu- ation of experimental data.