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International Concrete Abstracts Portal

Showing 1-5 of 476 Abstracts search results

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_07

Date: 

March 1, 2020

Author(s):

Eldon Tipping and Bryan M. Birdwell

Publication:

Symposium Papers

Volume:

338

Abstract:

This is the first of a three-part series, the goal of which is to provide the designer and contractor with tools necessary to produce deflected slabs on metal deck that are essentially level. This first part provides a general description of the components of a composite slab on metal deck including the behavior of each of the components prior to concrete placement and after the concrete hardens. Elements impacting the ability of the design/construction team to produce level deflected floors are presented and discussed. Fabrication tolerances for structural steel are published by the American Institute of Steel Construction (AISC) and impact the relative elevation of erected beam/column connections prior to concrete placement. Deflection of the erected floor frame under the weight of fresh concrete is impacted by choices made by the designer regarding the use of Allowable Strength Design (ASD) and Load and Resistance Factor Design (LRFD). Uncertain net deflections of the supporting structural steel frame provide challenges for the contractor in his efforts to provide sufficient concrete in the appropriate locations during initial strike-off to off-set the structural steel deflection. Implications of gauging up off the supporting structural steel versus using a rod and level for initial concrete strike-off are presented and discussed. The importance of construction joint location is addressed, and recommendations are presented.


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.


Document: 

SP-338_08

Date: 

March 1, 2020

Author(s):

Eldon Tipping and Bryan M. Birdwell

Publication:

Symposium Papers

Volume:

338

Abstract:

This is the second 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 second part explores the role ineffective and incorrect use of ACI and AISC documents plays in designer attempts to provide his client with level deflected slabs on metal deck. Project documents often incorrectly reference ACI guide documents such as ACI 302, attempting to make their content mandatory, when that is not intended by ACI. The ACI prohibition of using guide document content without restating in mandatory language is presented and discussed. Reference is often made in design documents to the AISC Code of Standard Practice for floor elevation when the Code is silent concerning the elevation of all elements excepting that of column base plate elevation. AISC tolerances impacting floor levelness are presented and discussed. Virtually all supporting structural steel floor framing systems are comprised of a collection of secondary members (beams) which transfer gravity loads to primary members (girders) which ultimately transfer these gravity loads to vertical elements and finally to foundations. The collection of floor framing members contains some combination of un-cambered steel beams/girders and those with fabricated camber to off-set anticipated deflection of the member when subjected to the weight of concrete. The deflection of those members will vary depending on member stiffness and the resistance of connections to end rotation. The ineffectiveness of the common designer requirement that concrete be added until “the floor is level” is presented and discussed in detail.


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