Ultimate Strength Of Concrete Research Articles

Experimental study on flexural toughness of fiber reinforced concrete beams: Effects of cellulose, polyvinyl alcohol and polyolefin fibers

Flexural toughnesses of concrete reinforced by cellulose fibers (CTFs), polyvinyl alcohol fibers (PFs) and polyolefin fibers (VSs) are studied through notched beam tests. Flexural strength, ultimate strength, residual flexural and tensile strength, fracture energy, the relationship between crack mouth opening displacement and deflection, as well as the synergistic effect of hybrid fibers are investigated. The results show the following. (1) With the increase of fiber dosage, CTFs enhance the flexural strength and ultimate strength of concrete, while high dosages of PFs and VSs weaken the flexural and ultimate strengths. (2) CTF-PF hybrid fibers have a positive synergistic effect on the flexural strength and ultimate strength of concrete. (3) With the increase of fiber dosage, CTFs firstly strengthen and then weaken the fracture energy of concrete, while PFs weaken and then strengthen the fracture energy, and VSs strengthen the fracture energy. CTF1.2PF2.0VS2.0 is considered the optimal combination of hybrid fibers. (4) It is significant that there is a three-stage linear functional relationship between the crack mouth opening displacement and deflection of fiber reinforced concrete.

Mesoscopic Fracture Model of Coarse Aggregate Interlocking Concrete

The skeleton formed by coarse aggregate has an important influence on the macroscopic mechanical properties of concrete, especially the fracture properties. Based on mesomechanics and fracture mechanics, this paper conducts theoretical simulations and experimental studies on the mechanical and fracture properties of coarse aggregate interlocking concrete through the theory of mesomechanics homogenization as well as compressive strength tests, flexural strength tests, axial compressive strength tests, elastic modulus tests, and fracture toughness tests. The results show that when the coarse aggregate is within a certain volume increase, the fracture energy and ultimate strength of concrete are significantly improved. At the same time, the proposed mesomechanics calculation model has high accuracy for calculating the fracture characteristics of concrete when the coarse aggregate increment is less than 20%.

Strengthening Prestressed Concrete Bridge Girders and Building Beams with Carbon Fiber Reinforced Polymer Sheets

The effect of Carbon Fiber Reinforced Polymer (CFRP) retrofitting and concrete type on the flexural strength of prestressed concrete I-section girders used in bridges and beams in buildings is investigated. Non-linear moment-curvature relationships are predicted using an iterative algorithm for both non-retrofitted and CFRP-retrofitted prestressed concrete girder and beam cross-sections with various concrete types. Two different CFRP-retrofitting schemes are analyzed for comparing their effectiveness. It is found that although non-retrofitted beam section exhibits greater ductility, the use of CFRP retrofitting in both tension and compression regions simultaneously results in a significant increase in flexural strength. It is also found that the higher the ultimate concrete strength, the higher is the influence of CFRP-retrofitting on increasing flexural strength.

Compressive behavior of concrete confined by CFRP and transverse spiral reinforcement. Part A: experimental study

This study presents the results of an experimental investigation of 18 short concrete columns confined by carbon fiber-reinforced polymer (CFRP) and transverse spiral reinforcement (TSR) under uniaxial compression. Longitudinal rebars are not installed in the specimens in order to eliminate their confinement effect to concrete which affects the analysis of 3-D compression of concrete. The paper only consider for FRP and spiral reinforcement confinement in transverse direction. Two key experimental parameters were investigated: the thickness of the CFRP tube (0.167, 0.334, and 0.501 mm) and the spacing of the TSR (25 and 50 mm). The failure mode, axial and transverse stress–strain relationship, confinement effectiveness, Poisson’s ratio and dilatation performance of the specimens were discussed. Test results show that the ultimate strength of concrete has a linear proportional enhancement with an increase in the FRP layer in each TSR category and a decrease in the TSR spacing in each FRP layer category. The ultimate load carrying capacity of the confined concrete depends on the confinement pressure during failure in terms of ultimate strength and axial strain.

Principal Component and Multiple Regression Analysis for Steel Fiber Reinforced Concrete (SFRC) Beams

This study evaluates the shear strength of steel fiber reinforced concrete (SFRC) beams from a database, which consists of extensive experimental results of 222 SFRC beams having no stirrups. In order to predict the analytical shear strength of the SFRC beams more precisely, the selected beams were sorted into six different groups based on their ultimate concrete strength (low strength with f c ′ < 50 MPa and high strength with f c ′ < 50 MPa ), span-depth ratio (shallow beam with a/d ≥ 2.5 and deep beam with a/d < 2.5) and steel fiber shape (plain, crimped and hooked). Principal component and multiple regression analyses were performed to determine the most feasible model in predicting the shear strength of SFRC beams. A variety of statistical analyses were conducted, and compared with those of the existing equations in estimating the shear strength of SFRC beams. The results showed that the recommended empirical equations were best suited to assess the shear strength of SFRC beams more accurately as compared to those obtained by the previously developed models.

The Experimental Research of low strength Concrete Considering Strain Rate under Uniaxial Compression

The tests were implemented in low strength concrete with four kinds of strength (C20, C25, C30, C35) and with diffrent strain ratses (10-5/s-1, 10-4/s-1, 10-3/s-1 and 10-2/s-1. The stress-strain curves, strength, elastic modulus and Poisson's ratio are studied in different strain rate. The results show that: (1) With the increase of strain rate, the inflexion strength and ultimate strength of concrete were improved; (2) With the increase of strain rate, the static and dynamic elastic modulus increased slightly; (3) Poisson's ratio increased slightly with the growth strain rate. This conclusion is very important in civil engineering.

The Experimental Research of Carbon Fiber Confined Concrete Considering Strain Rate under Uniaxial Compression

In the three kinds of constraint ratio (ξ = 0.065, ξ= 0.1025, ξ= 0.205), respectively, by the comparative analysis of 55 prism specimens using CFRP confined concrete(strain ratses are 10-5/s-1, 10-4/s-1, 10-3/s-1and 10-2/s-1), the stress-strain curves, strength, strain, elastic modulus and Poisson's ratio were studied at different constraints and different strain rate. The results show that: (1) with the strain rate increased,the inflexion strength and ultimate strength of concrete were improved; (2) with the strain rate increased, the static and dynamic elastic modulus increased slightly; (3) Poisson's ratio increased slightly with the growth strain rate.

Assessment of the effects of rice husk ash particle size on strength, water permeability and workability of binary blended concrete

This study develops the compressive strength, water permeability and workability of concrete by partial replacement of cement with agro-waste rice husk ash. Two types of rice husk ash with average particle size of 5 micron (ultra fine particles) and 95 micron and with four different contents of 5%, 10%, 15% and 20% by weight were used. Replacement of cement up to maximum of 15% and 20% respectively by 95 and 5 μm rice husk ash, produces concrete with improved strength. However, the ultimate strength of concrete was gained at 10% of cement replacement by ultra fine rice husk ash particles. Also the percentage, velocity and coefficient of water absorption significantly decreased with 10% cement replacement by ultra fine rice husk ash. Moreover, the workability of fresh concrete was remarkably improved by increasing the content of rice husk ash especially in the case of coarser size. It is concluded that partial replacement of cement with rice husk ash improves the compressive strength and workability of concrete and decreases its water permeability. In addition, decreasing rice husk ash average particle size provides a positive effect on the compressive strength and water permeability of hardened concrete but indicates adverse effect on the workability of fresh concrete.

Failure Mechanism of Concrete in Dynamic Loading

Understanding the dynamic behavior of concrete in rapid loading is an issue of great importance in civil engineering. In this study, an experimental program was performed to investigate the dynamic behavior of concrete subjected to different strain-rate loadings. From the test results the rate-dependent effect on the ultimate strength of concrete was confirmed, i.e., the strength increases with the increasing strain rate. The dynamic failure process of concrete in tension and physical mechanism were discussed based on the experimental observations.

Flexural behaviour of concrete beams reinforced with GFRP bars

This study presents the results of the comparison made between the predicted and the measured load-deflection relationships for 12 concrete beams reinforced either by steel or glass fibre reinforced plastic (GFRP) bars. The numerical part of the study was carried out using: (i) the computer model which accounts for the actual properties of the composite constituents developed as part of this study, (ii) the ACI load-deflection model, and (iii) the modified load-deflection model available in the literature for beams reinforced by FRP bars. The last two models were implemented on a spreadsheet. The deflection limit and the ultimate strength of concrete were the control parameters in design of the test beams. The computer model provides an accurate prediction of the measured service and full load-deflection curves. The errors in prediction of service load deflection and ultimate flexural strength are less than 10% and 1%, respectively. In the case of GFRP reinforced beams, the service load deflection predicted by the ACI model is in error by 70%, while that predicted by the modified model is in error by less than 15%.