Effect of Reinforcement on Early-Age Cracking in High Strength Concrete
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HERON, Vol. 49, No. 3 (2004)
Authors
M. S. Sule and K. van Breugel
Absract
During hydration, high strength concrete (HSC) is subjected not only to thermal effects but also to load-independent deformations, i.e. autogenous shrinkage. The additional autogenous shrinkage makes hardening HSC prone to cracking. As the prediction of the probability of cracking is solemnly based on the behaviour of concrete it was found that this is sometimes too pessimistic for reinforced HSC-structures. In order to investigate the stress development and the probability of cracking in hardening reinforced HSC, a Temperature Stress Testing Machine (TSTM) has been used for simulating the mechanical boundary conditions and for imposing different curing temperatures onto concrete specimens. The specimens were made of HSC and normal strength concrete (NSC). They were reinforced with different reinforcement percentages (0%, 0.75%, 1.34% and 3.02%) and configurations (one reinforcement bar and four reinforcement bars). It was found that four rebars in the corners of the test specimen postpone the moment of through-cracking, whereas specimens with one centrally placed rebar cracked almost as sudden as plain specimens. For quantifying the effect of reinforcement on the moment of cracking due to restrained load-independent deformations, a “strain enhancement factor” has been introduced. By applying the strain enhancement factor, the cracking probability of a reinforced HSC-structure can be estimated more realistically at early-age.
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RC Infilled Frame-RC Plane Frame Interactions for Seismic Resistance
Suyamburaja Arulselvan , K. Subramanian , E.B. Perumal Pillai and A.R. Santhakumar
Abstract: Experimental investigation was planned and conducted to study the influence of brick masonry infill in a reinforced cement concrete frame. The analytical methods available needs validation by comparison with experimental results and more accurate methods of analysis like finite element analysis has to be used for the above purpose. In this study, RC frame with middle bay brick infilled representing a five-stories, three bay building in quarter-scale has been taken for experimental investigation and the available methods of theoretical analysis and finite element analysis using ANSYS software for the frames have been carried out. Until the cracks developed in infills, the contribution of the infill to both lateral stiffness and strength was very significant. The change in lateral stiffness, strength, ductility and natural period of the framed structure due to the presence of infills change the behaviour of the building under seismic action. The object of this study was to investigate the behaviour of such infilled frames under seismic loads. For this purpose, five stories, three bay frames with central portion infilled with brick were tested under static cyclic loading simulating seismic action. Analytical works was done to understand the stiffness, strength and behaviour of these types of frames.
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Analysis and tests of rigidly connected reinforced concrete frames
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Title: Analysis and tests of rigidly connected reinforced concrete frames
Author: Abe, Mikishi
Subject: Reinforced concrete
Date: 1918
Publisher: University of Illinois at Urbana Champaign, College of Engineering. Engineering Experiment Station.
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Structural Steelwork: Design to Limit State Theory
Dennis Lam, Thien-Cheong Ang, Sing-Ping Chiew, "Structural Steelwork, Third Edition: Design to Limit State Theory"
Butterworth-Heinemann; 3 edition (March 18, 2004) | ISBN: 0750659122 | 368 pages | PDF | 2,2 Mb
This classic textbook is a comprehensive introduction to structural steelwork design.The book describes the design theory and code requirements for common structures, connections, elements and frames.
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*Updated to reflect the 2000 Amendment to Part 1 of BS5950.
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Disaggregated Seismic Hazard and the Elastic Input Energy Spectrum:
An Approach to Design Earthquake Selection
Martin C. Chapman
Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial
fulfillment of the requirements for the degree of
Doctor of Philosophy in Geophysics
J. Arthur Snoke, Chair
Gilbert A. Bollinger
Edwin S. Robinson
James R. Martin
Mahendra P. Singh
June 25, 1998
Blacksburg, Virginia
Keywords: Seismic Hazard, Strong Motion, Design Earthquakes, Input Energy
(Abstract)
The design earthquake selection problem is fundamentally probabilistic. Disaggregation of a probabilistic model of the seismic hazard offers a rational and objective approach that can identify the most likely earthquake scenario(s) contributing to hazard. An ensemble of time series can be selected on the basis of the modal earthquakes derived from the disaggregation. This gives a useful time-domain realization of the seismic hazard, to the extent that a single motion parameter captures the important time-domain characteristics. A possible limitation to this approach arises because most currently available motion prediction models for peak ground motion or oscillator response are essentially independent of duration, and modal events derived using the peak motions for the analysis may not represent the optimal characterization of the hazard.
The elastic input energy spectrum is an alternative to the elastic response spectrum for these types of analyses. The input energy combines the elements of amplitude and duration into a single parameter description of the ground motion that can be readily incorporated into standard probabilistic seismic hazard analysis methodology. This use of the elastic input energy spectrum is examined. Regression analysis is performed using strong motion data from Western North America and consistent data processing procedures for both the absolute input energy equivalent
velocity, (Vea), and the elastic pseudo-relative velocity response (PSV) in the frequency range 0.5 to 10 Hz. The results show that the two parameters can be successfully fit with identical functional forms. The dependence of Vea and PSV upon (NEHRP) site classification is virtually identical. The variance of Vea is uniformly less than that of PSV, indicating that Vea can be predicted with slightly less uncertainty as a function of magnitude, distance and site classification. The effects of site class are important at frequencies less than a few Hertz. The regression modeling does not resolve significant effects due to site class at frequencies greater than approximately 5 Hz.
Disaggregation of general seismic hazard models using Vea indicates that the modal magnitudes for the higher frequency oscillators tend to be larger, and vary less with oscillator frequency, than those derived using PSV. Insofar as the elastic input energy may be a better parameter for
quantifying the damage potential of ground motion, its use in probabilistic seismic hazard analysis could provide an improved means for selecting earthquake scenarios and establishing design earthquakes for many types of engineering analyses.
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