Flat slab strengthening techniques against punching-shear

Lapi, Massimo; Ramos, Aura; Orlando, Maurizio

doi:10.1016/j.engstruct.2018.11.033

Cited by 33 publications

(10 citation statements)

References 32 publications

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“…Nowadays, a significant number of flat slabs need to be strengthened [ 2 ]. This demand may arise from several factors that include construction or design errors, disobeying code provisions, environmental deterioration of materials, or increase in gravitational load [ 3 ]. Flat slabs are vulnerable to punching shear failure and many such circumstances have been reported [ 4 , 5 , 6 ].…”

Section: Introductionmentioning

confidence: 99%

Remediation of Punching Shear Failure Using Glass Fiber Reinforced Polymer (GFRP) Rods

et al. 2021

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The results of an experimental program on shear-strengthening of flat slabs using Glass Fiber Reinforced Polymer (GFRP) rods are presented. A total of seven specimens were tested under an upward concentric monotonic loading until failure. One specimen served as a control and was tested without any modification. The remaining six specimens were strengthened with post-installed GFRP rods in single (SG), double (DB), and radial (RD) patterns within shear critical parameters around the centric column. The results of this experimental study suggest that GFRP rods are capable of enhancing both the peak load and deformation capacity. Furthermore, brittle failure associated with punching shear failure was successfully avoided by all strengthening patterns. Of all of the patterns, the RD pattern resulted in maximum peak load increase and corresponding deformation capacity while the lowest bound was created by the SG pattern. The results suggested that SG, DB and RD patterns enhanced ultimate loads up to 9.1, 11.3 and 15.7% while corresponding deflections increased up to 109, 136 and 154%. Strain measurement on flexural reinforcement suggested that all strengthened specimens were able to withstand higher longitudinal strains than yield. It was further shown that reducing the spacing between the GFRP rods efficiently enhanced peak loads, nevertheless, neither this change was proportional, nor did it result in an enhanced energy dissipation capacity. In the end, recommendations of American Concrete Institute (ACI) for the shear strength of two-way systems were modified to incorporate the contributions from GFRP rods. The results indicate that the proposed analytical approach provides an excellent match with the experimental results.

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Section: Introductionmentioning

confidence: 99%

Remediation of Punching Shear Failure Using Glass Fiber Reinforced Polymer (GFRP) Rods

et al. 2021

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“…Similarly, numerical studies by Mohamed et al [45] observed that CFRP strengthening around openings located further from the supporting column enhances flexural capacity and overall stiffness of the slab. In fact, Lapi et al [46] believes that the increase in punching shear strength through strengthening of the flat slab using FRP strips is the indirect effect of the increase in slab stiffness due to the strengthening strips.…”

Section: Figure 14mentioning

confidence: 99%

Fiber Reinforced Polymer Laminates for Strengthening of RC Slabs against Punching Shear: A Review

2020

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Reinforced concrete flat slabs or flat plates continue to be among the most popular floor systems due to speed of construction and inherent flexibility it offers in relation to locations of partitions. However, flat slab/plate floor systems that are deficient in two-way shear strength are susceptible to brittle failure at a slab-column junction that may propagate and lead to progressive collapse of a larger segment of the structural system. Deficiency in two-way shear strength may be due to design/construction errors, material under-strength, or overload. Fiber reinforced polymer (FRP) composite laminates in the form of sheets and/or strips are used in structurally deficient flat slab systems to enhance the two-way shear capacity, flexural strength, stiffness, and ductility. Glass FRP (GFRP) has been used successfully but carbon FRP (CFRP) sheets/strips/laminates are more commonly used as a practical alternative to other expensive and/or challenging methods such column enlargement. This article reviews the literature on the methodology and effectiveness of utilizing FRP sheets/strips and laminates at the column/slab intersection to enhance punching shear strength of flat slabs.Polymers 2020, 12, 685 2 of 27 connection stiffness. The deflected profile in the slab compression region can be considered as straight lines, while that in the tension region shows a slight discontinuity, especially when the shear crack intersects the reinforcement. Moe [4] tested 43 slabs and investigated the results of 140 footings in addition to 120 slabs that are reported in the literature and noted the common appearance of inclined cracks at 60% of the ultimate load. These inclined cracks started from bending cracks, then rapidly extended up to the proximity of the neutral axis and finally developed rather slowly but leaving only a very narrow depth of the compression zone unaffected. During the structural design phase, if the shear capacity is exceeded, shear reinforcement can be designed to enhance the capacity. Some studies indicated that using shear reinforcement in two-way slabs may double the punching shear strength [5].Strengthening flat slabs at the column-slab juncture using externally applied material with high tensile strength did not start with the fiber reinforced polymer (FRP) sheets. Steel plates with steel anchor bolts were used successfully to increase the two-way shear strength of flat slabs. Ebead and Marzouk [6] strengthened slab-column junctions by installing on the tension side 6 mm thick American society for testing and materials (ASTM) A6 plates using 19 mm diameter ASTM A325 bolts. Steel plates increased the ultimate load of the flat slab by 45% when the applied load was central and by 122% when the specimens were subjected to both central loads and moments. The light weight, flexibility, and high tensile strength of FRP sheets and laminates make them viable alternative to steel plates. Externally bonded carbon fiber reinforced polymer (CFRP) sheets that are anchored to concrete at their ends were shown to inc...

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“…The theoretical predictions of the slab rotation at failure (ψ th ) are determined at the intersection between the failure criterion curve (equation ( 2)) and the load-rotation curve (equation ( 1)) for each specimen. The experimental slab rotations (ψ exp ) are derived from the vertical displacement measurements assuming a conical deformation of the slab outside the column region [39]. In particular the experimental rotations are calculated as ψ th = v/r, where v is the average vertical displacement in correspondence of the line of zero moments (see Figure 4) and r is the distance of this line from the column (in this case r=665 mm).…”

Section: Analytical Approachmentioning

confidence: 99%

Punching of reinforced concrete flat slabs – Rational use of high strength concrete

Inácio

Lapi

Ramos

2020

Engineering Structures

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Flat slab strengthening techniques against punching-shear

Cited by 33 publications

References 32 publications

Remediation of Punching Shear Failure Using Glass Fiber Reinforced Polymer (GFRP) Rods

Remediation of Punching Shear Failure Using Glass Fiber Reinforced Polymer (GFRP) Rods

Fiber Reinforced Polymer Laminates for Strengthening of RC Slabs against Punching Shear: A Review

Punching of reinforced concrete flat slabs – Rational use of high strength concrete

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