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International Concrete Abstracts Portal

Showing 1-5 of 30 Abstracts search results

Document: 

SP265-07

Date: 

October 1, 2009

Author(s):

J. Mazars, A. Rouquand, C. Pontiroli, P. Berthet-Rambaud, and Y. Malécot

Publication:

Symposium Papers

Volume:

265

Abstract:

The causes of the nonlinear behavior of concrete until failure are numerous and complex, particularly for nonmonotonic and rapid loadings. A model is presented coupling damage and plasticity including several effects: development and closure of cracks, damping, compaction, and strain rate effects. The idea is to describe, with the same tools, a wide variety of problems, the model is of explicit form, and what makes possible its implementation into explicit numerical scheme well adapted to the treatment of fast dynamic problems. In this context, the finite element "Abaqus explicit" code is used, and the model has been successfully applied during the past few years to model a large range of complex reinforced concrete structures subjected to severe loadings. In this paper, the main model concepts are presented, and some examples of numerical simulations are given and compared with experimental data. The applications proposed are related to quasi-static loading as well as to rapid loading (impact); in particular, one of them is within the framework of an experiment linked to the design of a reinforced concrete rock-shed gallery located in the French Alps. The results show the relevance of the modelling used, which makes some real numerical experiments very useful for complex structures and/or extreme loadings.

DOI:

10.14359/51663294


Document: 

SP265-19

Date: 

October 1, 2009

Author(s):

L.H. Sneed and J.A. Ramirez

Publication:

Symposium Papers

Volume:

265

Abstract:

This paper presents an evaluation of the minimum shear reinforcement requirements in the ACI 318 code for nonprestressed concrete beams exempt from distributed horizontal reinforcement requirements. A total of 34 tests performed by different researchers on reinforced concrete beams with heights in the range of 24 to 36 in. (600 to 900 mm) are used to examine the reserve shear strength defined as the shear strength in excess of the nominal shear strength provided by the concrete, Vc, calculated in accordance with ACI 318. Additionally, the design shear force limitations for these beams containing minimum shear reinforcement are examined. Tests evaluated in this study include beams without shear reinforcement as well as beams with shear reinforcement levels that are less than ACI 318-08 minimum requirements. From the evaluation conducted in this study, it is concluded that the addition of low amounts of shear reinforcement, even less than the minimum amount required by ACI 318-08, Vs,min, provide a reserve strength beyond Vc calculated in accordance with the code. Results also show that low amounts of shear reinforcement tend to eliminate the trend of decreasing shear strength with increasing height. When low levels of shear reinforcement are taken into account in the strength calculation (that is, Vn=Vc+ Vs,min), however, specific concerns are raised regarding the reliance on minimum shear reinforcement to mitigate low values of the concrete contribution to the shear strength as well as provide shear resistance above Vc without the use of the strength reduction f factor. Modifications to the minimum shear reinforcement requirement exceptions for beams in ACI 318-08 are also examined.

DOI:

10.14359/51663306


Document: 

SP265-22

Date: 

October 1, 2009

Author(s):

N.M. Hawkins and D.A. Kuchma

Publication:

Symposium Papers

Volume:

265

Abstract:

Five specific limitations to the existing shear design methodologies of the AASHTO LRFD Bridge Design Specifications and ACI 318-08 are discussed: (1) the issues resulting from the fact that what has been tested in the laboratory is not representative of what is built in the field for bridge structures and therefore where additional laboratory testing is needed particularly for bridge members; (2) the equivalency and non-equivalency of the treatment of axial load and prestress in shear provisions; (3) the basis for the minimum and maximum shear reinforcement requirements or limits for members and why those requirements differ in the AASHTO LRFD Specifications from those in ACI 318-08; (4) shear design considerations for the end regions of bridge girders and the need to design for the effects of the funneling of the shear force into the support and the balancing of the tension caused by shear at the face of the support; and (5) the relative variations in the components of the shear resistance with increasing load and changes in member behavior and the significance of those variations for the limitations to the existing shear design concepts of the AASHTO LRFD Specifications and ACI 318-08.

DOI:

10.14359/51663309


Document: 

SP265-13

Date: 

October 1, 2009

Author(s):

R.T. Mullapudi and A.S. Ayoub

Publication:

Symposium Papers

Volume:

265

Abstract:

This study presents an inelastic nonlinear beam element with axial, bending, and shear force interaction for cyclic analysis of reinforced concrete (RC) structures. The element considers shear deformation, and is based on the section discretization into fibers with hysteretic material models for the constituent materials. The shear mechanism along the beam is modeled by using a Timoshenko beam approach. The steel material constitutive law is assumed to be bilinear. The concrete constitutive law is based on the soften membrane model. This newly developed constitutive law can predict the concrete contribution Vc, which is produced by the shear resistance of concrete along the initial crack direction. The constitutive relationships of the RC element have been developed based on the smeared behavior of cracked continuous orthotropic material assumption of concrete with the inclusion of Poisson effects. This model accounts for the softening effect of concrete, as well as the tension stiffening and confining effects. Transverse strains are internal variables determined by imposing equilibrium at each fiber between concrete and vertical transverse steel reinforcement. Element forces are obtained by performing an equilibrium-based numerical integration on the section axial, flexural, and shear behaviors along the element length. The paper concludes with a correlation study between the analytical models and experimentally tested shear-critical RC columns.

DOI:

10.14359/51663300


Document: 

SP265-06

Date: 

October 1, 2009

Author(s):

L.M. Gil-Martín, E. Hernández-Montes, M.A. Aschheim, and S. Pantazopoulou

Publication:

Symposium Papers

Volume:

265

Abstract:

This paper provides a theoretical overview on the most influential theories for compression field models for shear and torsion. Special attention is given to the steel behavior because this is the point where the rotating-angle softened-truss model (RA-STM) and modified compression field theory (MCFT) depart. A new proposal for the steel model is presented. This proposal has the advantage of an embedded bar system, but it does not introduce additional complexity in the formulation. The steel model is based on tension stiffening behaviour. Several examples are presented, including a prestressed girder and a wall-type structure.

DOI:

10.14359/51663293


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