NOPR Collection:

Impact effect on different sized reinforced concrete specimens

Thu, 01 Oct 2015 00:00:00 GMT

Title: Impact effect on different sized reinforced concrete specimens Authors: Erdem, R Tuğrul; Gücüyen, Engin; Kantar, Erkan; Bağcı, Muhiddin Abstract: Behavior of structural members under various loads has been a major interest. However, impact loading type is the least known one among them. Researchers have investigated the behavior of structural members under impact effect recently. For this reason, a well-instrumented experimental program is used to understand the impact behavior of six different sized reinforced concrete specimens. All specimens both have longitudinal and transverse reinforcements. A testing apparatus is developed to perform tests under impact loading. Accelerometers, optic photocells, dynamic force sensor, a data logger and connecting cables are used as well as testing apparatus. Free falling height and mass of steel hammer are taken constant in the study. Test program has been successful to provide several data to understand the impact behavior. Drop numbers and rebound movements of the hammer are determined according to damage situations. Acceleration values are measured from four different points of the specimens. The change of velocity and displacement values is determined for all specimens. Impact force is also measured for each free falling movement and absorbed energy values are calculated according to the area under the curve of impact force-displacement graphs. Test results give substantial information about impact resistances of reinforced concrete members. Page(s): 597-603

Autogenous deformation of high performance concrete exposed to semi-adiabatic and isothermal conditions

Thu, 01 Oct 2015 00:00:00 GMT

Title: Autogenous deformation of high performance concrete exposed to semi-adiabatic and isothermal conditions Authors: Jiang, Chenhui; Yang, Yang; Hu, Qiaoying Abstract: This paper presents an experimental investigation on early-age autogenous deformation (AD) of high performance concrete (HPC) exposed to isothermal and semi-adiabatic conditions. A new testing apparatus equipped with eddy-current displacement sensors is used for monitoring deformation from final setting to 28 days. Deformation measurements are conducted on a series of HPC mixtures with different water-binder ratios (w/b) and cementitious materials. In order to accurately separate AD from the measured deformation, time-dependent coefficients of thermal expansion (CTEs) of HPC, other than a constant value, are employed. The results indicated that AD under semi-adiabatic condition is fundamentally different from the one under isothermal condition. The former undergoes three stages successively (i.e., initial rapid shrinkage, abrupt expansion and stable shrinkage stages), while the latter shows continuous shrinkage only. The considerable expansion under semi-adiabatic condition can be explained from delayed ettringite formation and thermal shock effect of early-age AD. Page(s): 587-596

Evaluation of high temperature effects on concrete-reinforcement bar bond using automated digital image processing

Thu, 01 Oct 2015 00:00:00 GMT

Title: Evaluation of high temperature effects on concrete-reinforcement bar bond using automated digital image processing Authors: Sezer, Gözde İnan; Sezer, Alper; Yazıcı, Şemsi Abstract: Behavior of reinforced concrete is strongly affected by bonding between concrete and reinforcing bar. It is well known that adherence among concrete and reinforcing bar is remarkably influenced by several properties of reinforced concrete including compressive strength, tensile strength and cover depth. On the other hand, adherence of reinforcing bar is influenced from cross-sectional dimension, embedment length, corrosion and curing conditions. Another significant parameter which adversely affects bonding between concrete and reinforcing bar is high temperature. Thereby, in this investigation, an experimental study is performed to assess the effect of high temperatures on several properties of reinforced concrete. Consequently, an attempt is made to establish correlations among the determined parameters designating the bonding between concrete and reinforcement bar. Additionally, image processing techniques are utilized to quantify the morphological properties of cracks occurred. It is found that, when temperature rises beyond 500^oC, behavior of reinforced concrete is dominated by bonding between concrete and reinforcing bar, rather than individual mechanical properties of concrete and reinforcing bar. Page(s): 581-586

Experimental, theoretical and numerical study on thin walled steel single and compound channel sections in axial compression

Thu, 01 Oct 2015 00:00:00 GMT

Title: Experimental, theoretical and numerical study on thin walled steel single and compound channel sections in axial compression Authors: Ananthi, G Beulah Gnana; Vishuvardhan, S; Knight, G M Samuel Abstract: This investigation presents a detailed description of experimental, theoretical and numerical studies of the flexural buckling strength of cold-formed steel (CFS) channel stub columns. A total of 24 single channels, double channels welded back to back and double channels welded as box sections both with and without lip stub columns are tested till failure with hinged ends and their behavior is studied. An attempt is made to study the effect of lip, and the effect of symmetricity of cross-section on the ultimate load carrying capacity. The flat width to thickness ratio of all the specimens are kept less than the limiting value as per IS 801-1975. Geometric and material non-linearity have been included in the finite element model. The design column strengths calculated using the finite element analysis (FEA) are compared with the IS: 801(1975), BS: 5950 (Part 5) and NAS manual. It is shown that the design column strengths calculated based on the codal specifications generally are conservative with experimental and numerical strengths. Page(s): 570-580