دانلود رایگان مقاله تفسیر پدیدارشناسی رفتار برشی تیرهای مهندسی سیمانی کامپوزیت

Abstract

This paper describes an experimental investigation of the shear behavior of beams consisting of steel Reinforced Engineered Cementitious Composites (R/ECC). This study investigates and quantifies the effect of ECC's strain hardening and multiple cracking behavior on the shear capacity of beams loaded in shear. The experimental program consists of R/ECC beams with short (8 mm) randomly distributed Polyvinyl Alcohol (PVA) fiber and conventional Reinforced Concrete (R/C) counterparts for comparison with varying shear reinforcement arrangements. Beams were loaded until failure while a Digital Image Correlation (DIC) measurement technique was used to measure surface displacements and crack formation. The shear crack mechanisms of R/ECC are described in detail based on findings of DIC measurements and can be characterized by an opening and sliding of the cracks. Multiple micro-cracks developed in a diagonal arrangement between the load and support points due to the strain-hardening response of ECC in tension. The strain-hardening response strongly influenced the shear response of the beam specimen.

7. Conclusions and remarks

The benefits of R/ECC, regards to resisting shear, include improved shear resistance and cracking control. Similar to uni-axial tension, multiple cracking of ECC occurs in shear. The first cracking strength was slightly higher for the R/C used in this study; however, the initial crack opening of the R/C was 10 times larger than that in the R/ECC. Crack deformations for the R/ECC were between 3 and 5 times smaller than for R/C at similar load levels. The addition of stirrups in R/C controls cracks widths as more stirrups resulted in reduced initial crack opening and total crack deformations (opening and sliding). Initial crack opening was independent of stirrup spacing in the R/ECC beams. The contributions of ECC on shear behavior of R/ ECC include:  Fiber bridging of shear crack, thus increasing the shear capacity;  Traditional shear reinforcement is activated at smaller individual crack deformations;  Crack deformations are limited by fiber bridging mechanism and by activating traditional shear reinforcement at smaller crack deformations. Based on the shear stress-strain responses and DIC measurements of the specimen deformations, a phenomenological descriptions of the shear crack opening, crack sliding and subsequent failure of R/C and R/ECC are proposed. For the R/C the shear loads over the shear crack can be transferred only by stirrups, aggregate interlock and fiber dowel effect of longitudinal reinforcement. The crack development mechanism for R/ECC is more complex due to the fiber bridging mechanisms, which induces multiple cracking resulting in smaller crack openings at a given shear stress as well as higher peak shear stress. The experimental program demonstrated that the use of R/ECC provides improved shear resistance, better control of crack sizes, and a more ductile shear failure than R/C. However, shear stress transfer over the crack via aggregate interlock is significantly reduced in ECC type materials due to the small particle size in the matrix. Additional increases in shear failure ductility of ECC would be possible by using fibers that can resist higher shear deformations and engineering the composite to fail by fiber pullout rather than rupture.