جستجو در تالارهای گفتگو

ANCHORAGE OF HIGH-STRENGTH REINFORCING BARS WITH STANDARD HOOKS By Ali Ajaam Submitted to the graduate degree program in Civil, Environmental, and Architectural Engineering and the Graduate Faculty of the University of Kansas in partial fulfilment of the requirements for the degree of Doctor of Philosophy Date Defended: April 3, 2017 ABSTRACT Hooked bars are often used to anchor reinforcing steel where concrete dimensions are not sufficient to provide the required development length for straight reinforcement, such as in external beam-column joints. The purpose of this study is to expand the understanding of the behavior of hooked bars in high-strength concrete and to develop design guidelines allowing for the use of high-strength reinforcing steel and high-strength concrete. In this study, 122 simulated beam-column joints were tested as a continuation of previous work at the University of Kansas. The test parameters included bar size (No. 5, No. 8 and No. 11), hook bend angle (90° or 180°), embedment length (5.5 to 23.5 in.), amount of confining reinforcement within the joint (no confining reinforcement to nine No. 3 hoops), location of the hooked bar with respect to member depth, hooked bar stresses (22,800 to 138,800 psi), concrete compressive strength (4,490 to 14,050 psi), center-to-center spacing between hooked bars (2 to 11.8db), number of hooked bars (2, 3, 4, or 6), arrangement of hooked bars (one or two layers), and ratios of beam effective depth to embedment length (0.6 to 2.13). Some specimens contained strain gauges mounted along the straight portion of the hooked bars and on the confining reinforcement within the joint rejoin. Test results from this study, along with test results from earlier work covering specimens without and with confining reinforcement, concrete compressive strengths between 2,570 and 16,510 psi, and bars stresses at anchorage failure ranging from 22,800 and 144,100 psi, were used to develop descriptive equations for the anchorage strength of hooked bars. The results of this study show that the current Code provisions overestimate the contribution of the concrete compressive strength and the bar size on the anchorage strength of hooked bars. The incorporation of the modification factors for cover and confining reinforcement in the provisions in the ACI Building Code (ACI 318-14) produces an unconservative estimation of anchorage strength of hooked bars, particularly with large hooked bars and closely-spaced hooked bars (hooked bars with center-to-center spacing less than 6db). Closely-spaced hooked bars exhibit less anchorage strength than widely-spaced hooked bars. The reduction in anchorage strength of closely-spaced hooked bars is a function of both the spacing between hooked bars and the amount of confining reinforcement. Both the hooks and the straight portion of hooked bars contribute to anchorage strength. The anchorage strength of staggered hooked bars can berepresented by considering the minimum spacing between the bars. Hooked bars anchored in beam-column joints with ratio of beam effective depth to embedment length greater than 1.5 exhibit low anchorage strengths compared to hooked bars with a ration below 1.5. These observations are used to develop proposed Code provisions for the development length of reinforcing bars anchored with standard hooks. The proposed provisions provide a higher level of reliability than current provisions and can be used for reinforcing steels with yield strengths up to 120,000 psi and concretes with compressive strengths up to 16,000 psi. Keywords: anchorage , beam-column joints, bond and development, concrete, high-strength concrete, high-strength steel, hooks, closely-spaced hooks, staggered-hooks, reinforcement, reinforcement strain منبع Ajaam_ku_0099D_15173_DATA_1.pdf

Control of Deflection in Concrete Structures ACI 435R-95 Reported by ACI Committee 435 This report presents a consolidated treatment of initial and time-dependent deflection of reinforced and prestressed concrete elements such as simple and continuous beams and one-way and two-way slab systems. It presents the state of the art in practice on deflection as well as analytical methods for computer use in deflection evaluation. The introductory chapter and four main chapters are relatively independent in content. Topics include “Deflection of Reinforced Concrete One-way Flexural Members,” “Deflection of Two-way Slab Systems,” and “Reducing Deflection of Concrete Members.” One or two detailed computational examples for evaluating the deflection of beams and two-way action slabs and plates are given at the end of Chapters 2, 3, and 4. These computations are in accordance with the current ACI- or PCI-accepted methods of design for deflection. Keywords: beams; camber; code; concrete; compressive strength; cracking; creep; curvature; deflection; high-strength concrete; loss of prestress; modulus of rupture; moments of inertia; plates; prestressing; pretensioned; post-tensioned; reducing deflection; reinforcement; serviceability; download ACI435.pdf

چند فایل پاورپوینت آموزشی در زمینه ضوابط آیین نامه ACI Building Code Requirements for Structural Concrete (ACI 318M-11) Overview of ACI 318M این پاورپوینتها به شرح زیر هستند: Design of Prestressed Concrete Evaluation of Existing Structures لینک دانلود Analysis and Design for Flexure, Shear, Torsion, and Compression plus Bending لینک دانلود Design of Slender Columns by ACI 318 لینک دانلود Design of Wall Structures by ACI 318 لینک دانلود Design of Structures with High-Strength Concrete by ACI 318 لینک دانلود فایلها از پیوست هم قابل دانلود است به نقل از ابرسازه ها ACI VN 2011 Topic 1.rar ACI VN 2011 Topic 3.rar ACI VN 2011 Topic 2.rar ACI VN 2011 Topic 4.rar ACI VN 2011 Topic 5.rar

Evaluation of Autogenous Shrinkage in High-Performance Concrete Jamal Ahmadi; Reza Naghdi2 Recent tendencies in concrete technology have been towards to high- performance concrete with a low water-cement ratio. However, high performance concretes have some problems. One of the problems is early-age cracking due to autogenous shrinkage. This study presents the results of an experimental investigation carried out to evaluate the autogenous shrinkage of high-strength concrete. According to this, effects of water/binder ratio, cement content, fine to coarse aggregate ratio and silica fume content were evaluated. From the results of this investigation, it can be concluded that the autogenous shrinkage strain of high strength concrete increases with reduction of w/b ratio. The results show also that the variation of cement content and fine to coarse aggregate ratio had only a limited effect on the autogenous shrinkage. منبع دانلود JSEG581419885000.pdf