Yield Strength Of Steel Bars Research Articles

Development of strength models for brick walls: Experimental and theoretical study

The low cost of cement-clay interlocking (CCI) bricks is an attractive feature, resulting in a wide utilization of CCI bricks in the construction of masonry walls. Despite this, an experimental database on the performance of CCI brick walls is scarce. This study tested ten large masonry walls constructed with CCI bricks in a running bond pattern. Two types of CCI bricks were used to assess the effect of chemical position on the diagonal compressive capacity of walls. Further, different grouts and steel bars were used within the openings in CCI bricks. A combination of grout and steel bars resulted in the optimal improvement of the diagonal compressive strength, whereas up to 110% higher improvement in the diagonal compressive strength was achieved by doubling the compressive strength of grout. Interestingly, the type of bricks did not influence the improvement in the diagonal compressive capacity of CCI brick masonry walls. A regression-based equation was proposed to predict the diagonal compressive capacity of CCI brick walls by including the yield strength of steel bars, the compressive strength of grout, and the diagonal compressive strength of ungrouted walls as explanatory variables. The predicted capacities of CCI brick walls were found to be in close agreement with experimental results.

Full-scale experimental study on continuous UHPC slabs of steel-UHPC composite deck system

The heavy self-weight and the cracking of normal strength concrete (NSC) deck slabs hindered the application of steel-concrete composite girders in long-span bridges. These problems can be solved by using ultra-high performance concrete (UHPC) deck slabs instead of the NSC deck slabs. Based on Yellow River Bridge of Zhanhua-Linzi Highway, a steel-UHPC composite cable-stayed bridge with span length of 442 m, full-scale tests on seven continuous UHPC (NSC) deck slabs were conducted. The studied parameters were sagging-to-hogging reinforcement ratio, concrete type, yield strength of steel bars and wet joints. The static properties of continuous UHPC (NSC) deck slabs were investigated in detail, including failure modes, load-deflection response, cracking behavior, strain development and moment redistribution. Discussions were made on the effect of different parameters according to the experimental data. Results showed that the use of UHPC can avoid shear failure, which was the case for the continuous NSC slab. Reducing the sagging-to-hogging reinforcement ratio from 1.00 to 0.63, the failure mode changed due to the altered formation order of plastic hinges. The ultimate capacity was decreased while the ductility and moment redistribution were improved by decreasing the yield strength of steel bars. The existence of wet joints significantly weakened the deck slabs. Strengthening the wet joints with steel plates can effectively compensate for this effect and even achieve better mechanical properties compared with integrally cast slabs. Furthermore, placing a comb-shaped wet joint at the intermediate support of continuous slab will result in a certain decrease of ultimate capacity and stiffness, which is acceptable for the transverse direction with relatively small internal forces. It is suggested that wet joints should be avoided at the supports of continuous deck slabs along the longitudinal direction.

Effect of Inclination of Rectangular Reinforced Concrete Short Columns on the Confinement

The main objective of this paper is to study the confinement of the rectangular reinforced concrete short inclined columns. This paper was based on theoretical analysis using the MATLAB program according to Universal Codes, and variables that were carefully selected to be the most influential factor. The angle of the inclination (α) was taken as a major variable in the paper, in addition other variables which in turn affect directly on the behavior of inclined columns such as the percentage of reinforcing steel in the concrete section of the column (ρ), the compressive strength of the concrete (fʹc), yield strength of steel bars (fy) and effective depth ratio (γ). The results show that best ratio of reinforcing steel that improves the value of the confinement ranges from 0.4 - 0.6 which leads to an increase in the confinement of (60 – 100) %, and these rates increase with increasing α, and the increase in fʹc leads to a significant increase in the confinement, especially when HSC is used..On the other hand, decreasing fy leads to increase in confinement, and the value of the γ had a considerable effect on the confinement that was decreased by about 11% when γ equals 0.9, compared with the corresponding γ equals 0.6.

Experiment on axial compression performance of glass fiber reinforced polymer-walled concrete-filled steel tube columns

In order to study the axial compression performance of glass fiber reinforced polymer (GFRP)-walled concrete-filled steel tube columns, the static axial compression tests were conducted on a group of non-GFRP constrained specimens and two groups of GFRP constrained specimens. According to the test results, a strong and weak constraint model of the wall column was proposed. Based on the twin-shear unified strength theory, the formula was established to calculate the axial compression bearing capacity of the GFRP-walled concrete-filled steel tube columns. Finally, the theoretical results, obtained through the establishment of the finite element model, were compared with the experimental results. And a parametric analysis was used to study the effect of the yield strength of steel and the strength of concrete on the axial compression performance of the new type wall-filled concrete-filled steel tube columns. The results show that the wall-filled concrete-filled steel tube columns eventually fail due to crushing of the concrete, buckling of the steel tube and excessive deformation of the specimens. At the beginning of the second linear section of the specimen, the steel begins to yield and its strength is fully exerted, which demonstrates that GFRP can effectively improve the peak load of the member, however, the ductility has decreased. The results of the theoretical formula are in agreement with the experimental results. The bearing capacity can be improved by increasing the strength of concrete and the yield strength of the steel. Compared with the strength of concrete, the yield strength of steel bars has a greater influence on the bearing capacity.

Residual Mechanical Properties and Constitutive Model of High-Strength Seismic Steel Bars through Different Cooling Rates.

In this study, the high-temperature test (i.e., temperature to 1000 °C) is conducted on 600 MPa seismic steel bars, and its residual mechanical properties and constitutive relations are investigated though three cooling rates, i.e., under air, furnace, and water-cooling conditions. Results show that three cooling methods have significant effects on the apparent characteristics of 600 MPa steel bars, when the heating temperature is greater than 600 °C. In addition, the ultimate and yield strength of steel bars have been significantly affected by different cooling methods, with increasing heating temperature. However, the elastic modulus is significantly not affected by temperature. Furthermore, the elongation rate after fracture and the total elongation rate at the maximum force do not change significantly, when the heating temperature is less than 650 °C. The elongation rate, after fracture, and the total elongation rate, at the maximum force, have different changes for three cooling methods. The degeneration of the stress–strain curves occurs when the heating temperature is high. The two-fold line, three-fold line, and Ramberg–Osgood models are developed based on the stress–strain curve characteristics of steel bars after cooling. The fire resistance of 600 MPa steel bars of reinforced concrete structure is analyzed, which provides a basis for post-disaster damage assessment, repair, and reinforcement of the building structure.

Fractional factorial design model for seismic performance of RC bridge piers retrofitted with steel-reinforced polymer composites

This study explores the effects of key design parameters on the performance of seismically deficient rectangular cross-section reinforced concrete (RC) bridge piers strengthened with steel-reinforced polymer (SRP) composites. Nonlinear response of bridge piers was modeled using fiber-based section discretization. Three-level fractional factorial design of experiments at 5% significance level was used to capture the effects of design parameters and their interactions, including concrete compressive strength, yield strength of steel bars, geometric ratio of longitudinal bars, internal transverse reinforcement spacing, pier aspect ratio, and number of retrofitting SRP layers. A parametric study was used to examine the main influence of and interactions between these factors on the seismic performance of SRP-strengthened piers at different damage limit states, including concrete core crushing, longitudinal reinforcement yielding and buckling, and ductility performance. Results show that the lateral load-carrying capacity and ductility performance of SRP-confined RC bridge piers were significantly influenced by the pier aspect ratio, materials properties, and amount of transverse and longitudinal reinforcement. Moreover, the resistance to buckling base shear, and overall ductility increased with increasing number of SRP layers.

Convex model-based calculation of robust seismic fragility curves of isolated continuous girder bridge

The convex model approach is applied to derive the robust seismic fragility curves of a five-span isolated continuous girder bridge with lead rubber bearings (LRB) in China. The uncertainty of structure parameters (the yield force and the post-yield stiffness of LRB, the yield strength of steel bars, etc.) are considered in the convex model, and the uncertainty of earthquake ground motions is also taken into account by selecting 40 earthquake excitations of peak ground acceleration magnitudes ranging from 0.125 to 1.126 g. A 3-D finite element model is employed using the software package OpenSees by considering the nonlinearity in the bridge piers and the isolation bearings. Section ductility of piers and shearing strain isolation bearings are treated as damage indices. The cloud method and convex model approach are used to construct the seismic fragility curves of the bridge components (LRB and bridge piers) and the bridge system, respectively. The numerical results indicate that seismic fragility of the bridge system and bridge components will be underestimated without considering the uncertainty of structural parameters. Therefore, the failure probability P f,max had better be served as the seismic fragility, especially, the fragility of the bridge system is largely dictated by the fragility of LRB. Finally, the probabilistic seismic performance evaluation of the bridge is carried out according to the structural seismic risk estimate method.

Shear strength reduction due to introduced opening in loaded RC beams

The reduction of shear strength due to the introduction of an opening is an ongoing problem for reinforced concrete (RC) beams. Fifteen rectangular section (150mm × 300mm × 1650mm) specimens were tested and divided into six groups under three considerations: 1) opening dimensions and shape, 2) time needed to create an opening for a new or an existing building; 3) external and internal strength of the opening in RC beams. The results demonstrate that a reduction in stiffness occurs due to the presence of an opening. The stiffness reduces further when the opening is placed under loading because of the reduction in the effective moment of inertia due to formation cracks around the opening as a result of the opening process. The stirrups besides the opening resisted shear force with ratios between 35% and 65% from the yield strength of steel bars and must be considered for shear resistance. Finally, the initial proposal equation that calculates the resistance shear force taken by the vertical stirrups around the opening can serve as a guideline for the introduction of an opening in RC beams.

Performance Enhancement of TMT Rebar in Accelerated Corrosion

Thermo-Mechanically-Treated (TMT) bars have recently been used as advancement over the conventional mild steel bars in reinforced concrete structures in order to enhance the durability in corrosive environment. Corrosion of steel reinforcement leads to cracking of reinforced concrete sections and thus may further reduce the load carrying capacity and serviceability of the structural members. Corrosion of rebars may cause reduction in yield strength of steel, affect the bond strength due to delamination of rust formed on the rebar surface. In this paper, the results of an experimental investi- gation on effects of corrosion on the mechanical strength of TMT steel rebars are presented. Corrosion is induced on the bars by impressed current method. The rebars are subjected to varying levels of corrosion and their stress strain characteris- tics are studied. The stress strain characteristics indicate a decrease in the area under stress strain curve with increasing level of corrosion. Further, it is observed that the yield strength of steel bars is not affected at a lower percentage of corro- sion, but for higher percentage of corrosion there is a considerable reduction in yield strength, percentage of elongation. It was also observed that at a higher percentage of corrosion the failure pattern of bars had changed from ductile mode to brit- tle mode.