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International Concrete Abstracts Portal

Showing 1-5 of 30 Abstracts search results

Document: 

SP265-23

Date: 

October 1, 2009

Author(s):

G. Birkle and W.H. Dilger

Publication:

Symposium Papers

Volume:

265

Abstract:

Solid slabs supported directly on columns offer elegant solutions for short span bridges. For buildings, flat slabs are becoming more and more popular. Solid slabs are easy and economical to construct, and for buildings they offer ease of mechanical installations and maximum story height. The slab thickness is primarily governed by deflection/vibration limits or punching shear. The latter may lead to a very brittle and sudden type of failure that can be avoided by increasing the slab thickness, using high-strength concrete, or providing shear reinforcement. The most effective of these is shear reinforcement because it deals directly with the localized problem of punching and it also prevents brittle failure. The main challenges of shear reinforcement are the installation and the anchorage of the shear elements. These problems are most adequately solved by using headed studs mounted on rails. To investigate the effect of layout and the extent of the shear reinforcement on the punching shear resistance, six slab-column connections were tested at the University of Calgary. The tests showed that the strength of the connections and their ductility were significantly enhanced by shear stud reinforcement. They also demonstrated that the radial layout of the studrails as required by Eurocode 2 exhibited no advantage in performance over an orthogonal layout where the studrails were aligned with the orthogonal reinforcing mesh. This is the standard arrangement in North America. The latter is preferable because of the minimal interference with the non-prestressed or prestressed flexural reinforcement. In the present test series, maximum ductility was achieved by extending the shear reinforcement to 4d from the face of the column. Where the shear reinforcement was only extended to 2d from the face of the column, an increase in strength was recorded, but the mode of failure still had to be classified as brittle because the failure surface occurred outside the shear reinforced zone. Providing shear studs spaced at d/2 to a distance 2d from the column and spaced at d between 2d and 4d significantly increased the ductility of the connection. Ductile behavior is especially important for the performance of slab-column connections of bridges and buildings in seismically active zones.

DOI:

10.14359/51663310


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: 

SP265-14

Date: 

October 1, 2009

Author(s):

L. Elfgren

Publication:

Symposium Papers

Volume:

265

Abstract:

The paper describes the development of models for torsion in northern Europe. After an introduction with a few historical notes, early use of nonlinear methods in Scandinavia is presented. The development of failure models for combined torsion, bending and shear is then described as well as the use of truss models. Static and kinematic methods are treated and a discrepancy in the results from different approaches is discussed. A refined model is then presented which unifies the results. Finally, some recent contributions are presented regarding prestressed high-strength circular column elements, hollow core slabs and curved bridges.

DOI:

10.14359/51663301


Document: 

SP265-01

Date: 

October 1, 2009

Author(s):

R.D. Lequesne, G.J. Parra-Montesinos, and J.K. Wight

Publication:

Symposium Papers

Volume:

265

Abstract:

Results from the test of a large-scale coupled-wall specimen consisting of two T-shaped reinforced concrete structural walls joined at four levels by precast coupling beams are presented. Each coupling beam had a span length-depth ratio (ln/h) of 1.7, and was designed to carry a shear stress of 7vfc' [psi], (0.59vfc' [MPa]). One reinforced concrete coupling beam was included along with three strain-hardening, high-performance fiber-reinforced concrete (HPFRC) coupling beams to allow a comparison of their behavior. When subjected to reversing lateral displacements, the system behaved in a highly ductile manner characterized by excellent strength retention to drifts of 3% without appreciable pinching of the lateral load versus drift hysteresis loops. The reinforced concrete structural walls showed an excellent damage tolerance in response to peak average base shear stresses of 4.4vfc' [psi], (0.34vfc' [MPa]). This paper presents the observed damage patterns in the coupling beams and the structural walls. The restraining effect provided by the structural walls to damage-induced lengthening of the coupling beams is discussed and compared with that observed in component tests. Finally, the end rotations measured in the coupling beams relative to the drift of the coupled-wall system are also presented.

DOI:

10.14359/51663288


Document: 

SP265

Date: 

October 1, 2009

Author(s):

Editors: Abdeldjelil Belarbi, Y.L. Mo and Ashraf Ayoub / Sponsored by: Joint ACI-ASCE Committee 343 and Joint ACI-ASCE Committee 445 and Joint ACI-ASCE Committee 447

Publication:

Symposium Papers

Volume:

265

Abstract:

This CD-ROM consists of 29 papers that were presented at technical sessions sponsored by Joint ACI Committees 343, 445, and 447, at the ACI Fall 2009 Convention in New Orleans, LA, in November 2009. The papers represent state-of-the-art advances in knowledge on shear and torsion. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-265

DOI:

10.14359/51663324


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