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International Concrete Abstracts Portal

Showing 1-5 of 478 Abstracts search results

Document: 

SP-343_36

Date: 

October 1, 2020

Author(s):

Amin, A.; Gilbert, R.I.

Publication:

Symposium Papers

Volume:

343

Abstract:

A significant body of research is available on the strength of steel fibre reinforced concrete (SFRC) members subjected to shear and flexure. The behaviour of SFRC under service loads has received less research attention. As the fibres are capable of transmitting tensile stress across a crack, the average tensile strain at a crack in a reinforced concrete member containing fibres is less than that in a similar member without fibres. As a result, the cracking and deformation characteristics of reinforced concrete structures can be significantly improved by adding fibres to the concrete mix. This paper first describes a physically rationale model of the tension stiffening behaviour of SFRC. With this behaviour quantified, expressions suitable for the design of SFRC members are derived for the control of instantaneous deflections and crack widths. Finally, a short example is provided.


Document: 

SP-343_42

Date: 

October 1, 2020

Author(s):

Fargier-Gabaldon, L.B.; Al-Tameemi, M.; Parra-Montesinos, G.J.

Publication:

Symposium Papers

Volume:

343

Abstract:

The effect of discontinued, randomly distributed steel fibers on the effective moment of inertia (𝐼!) of lightly reinforced flexural members is evaluated through the testing of three pairs of specimens under four-point bending. The specimens consisted of a simply supported, 3660 mm long, 254 mm deep, and 610 mm wide one-way slab strip. All slab specimens contained minimum flexural reinforcement according to the ACI 318-14 Building Code. The first pair featured regular concrete (no fibers), while the second and third pairs included steel fibers in a volume fraction (𝑉") of 0.26% and 0.38%, respectively. Beyond cracking, a substantial drop in the flexural stiffness was noticed in all specimens. The slabs with fibers, however, exhibited stiffer post-cracking response compared to their regular concrete counterparts. At yielding, a well-distributed cracking pattern was noticed in all test slabs, with maximum cracks widths of approximately 0.5 mm. It was found that the equation proposed by Bischoff (2005) to estimate the effective moment of inertia for concrete beams fits well the experimental data of the fiberreinforced concrete slabs, given that the stiffening factor is set equal to one.


Document: 

SP-342_08

Date: 

June 1, 2020

Author(s):

Faress Hraib, Li Hui, Brandon Gillis, Miguel Vicente, and Riyadh Hindi

Publication:

Symposium Papers

Volume:

342

Abstract:

During bridge construction, the concrete finishing machine weight, along with other dead and live loads, affects the stability of the structure during construction and the service life of the bridge. These eccentric unbalanced loads lead to torsional moments in the exterior girders of the bridge, deflection of the overhang, and excessive rotations in the exterior girders. In skewed bridges, the finishing (screed) machine can be oriented parallel to the skew or perpendicular to the girders during construction. This study focused on evaluating different orientations of the machine along the span of skewed bridges. Finite element models of bridges with different skew angles were developed using SAP2000 to simulate construction conditions. These bridge models were then subjected to different machine orientations to form a better understanding of this phenomenon and to find the most effective method to operate the concrete finishing machines. The results showed that moving the screed machine parallel to the skew angle led to rotations that were more balanced between the exterior girders compared to moving it perpendicular to the girders. Therefore, a more leveled concrete surface can be obtained when running the machine parallel to the skew.


Document: 

SP-340-10

Date: 

April 1, 2020

Author(s):

Santosh Timilsina, Nur Yazdani, Eyosias Beneberu, and Abel Mulenga

Publication:

Symposium Papers

Volume:

340

Abstract:

Fire is a possible hazard on highway bridges which causes significant economic damage, and it is also one of the least investigated of all hazards. There is a lack of knowledge on the long term performance and structural integrity of fire damaged and fiber reinforced polymer (FRP) laminate retrofitted bridges. One such rare in-service bridge was selected for this study. The fire damaged cast-in-place non-prestressed girders were previously repaired with mortar and strengthened with FRP wrapping. The girders were instrumented with strain gages and displacement transducers, and a non-destructive live load test was carried out to evaluate the structural response. The results from the load testing were used to compare two identical girder spans with and without CFRP strengthening. A full-scale non-linear finite element model of the overall bridge superstructure was created, and the test results used to calibrate the model. The carbon (CFRP) strengthened girder exhibited similar stiffness compared to the undamaged girder as evidenced by almost equivalent mid-span deflection. The girder moment capacity decreased significantly due to fire damage, and the CFRP strengthening plus mortar repair was successful in restoring the moment capacity. The finite element model provided good correlation with load test results.


Document: 

SP-338_09

Date: 

March 1, 2020

Author(s):

Eldon Tipping and Bryan M. Birdwell

Publication:

Symposium Papers

Volume:

338

Abstract:

This is the third of a three-part series, the goal of which is to provide the designer and contractor with tools necessary to produce level deflected slabs on metal deck. This third part provides the designer and contractor with strategies for producing level deflected slabs on metal deck. An approach by which elevation tolerances can be successfully imposed on the erected steel frame is presented. The method requires that the designer first provide the contractor with desired relative elevation of splice points at each floor level and flexible column splice details. This information, provided by the designer, enables the contractor to establish desired relative elevations that can assist in achieving those tolerances. An effective cambering strategy that recognizes the differing behavior of members framing to columns and those that connect to girders is presented and discussed. The paper finally presents a floor construction/monitoring program that identifies frame behavior during construction and provides both the designer and contractor with the resources necessary to produce level deflected slabs. The program includes pre- and postplacement surveys of structural steel frame, utilization of a controlled method of striking off the concrete, a survey of the completed slab surface, and use of the collected data to respond to unexpected structural behavior. Other tools, including the selective use of “loose shores” or a secondary placement can enable the contractor to produce deflected slabs on metal deck with 80% or more of the surface within a 3/4 inch (19 mm) deep envelope.


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