Abstract This work presents an experimental study concerning the post-punching behaviour of flat slabs strengthened with a new technique based on post-tensioning with anchorages by bonding using an epoxy adhesive. This strengthening technique proved efficient with respect to ultimate and serviceability states. Five slab specimens were tested in the post-punching range and it was found that the post-punching resistance was on average 78% of the punching resistance. This paper reports the development of strand forces and slab displacements from the beginning of the tests, including the bond stresses developed at several stages of the loading process. It was observed that top reinforcement bars were capable of transmitting post-punching loads to the prestressing strands. Taking this into account and based on the load bath envisaged from the column to the slab, expressions for the vertical load capacities corresponding to the parts of the load path are presented and compared with the experimental results, showing their ability to predict both ultimate loads and modes of failure. Compared with other strengthening techniques, the one proposed here not only upgrades ultimate and serviceability behaviour but also adds post-punching resistance, which is a great advantage in the event of progressive collapse, since it may avoid the collapse of an entire structure, thus reducing the risk of material and human losses.
Last. A. Pinho Ramos(NOVA: Universidade Nova de Lisboa)H-Index: 7
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This work aims to study a new flat slab strengthening technique based on post-tensioning with anchorages by bonding using an epoxy adhesive. The main advantages of this technique over the traditional prestress strengthening systems that use mechanical anchorages are that it does not need external permanent anchorages, meaning that the forces are introduced into the concrete gradually instead of being localized, thereby preserving aesthetics and useable space. The seven tested slab models show th...
The objective of this study was to analyse the behaviour of prestress strand anchorages by bonding with an epoxy adhesive for structural strengthening use. Pull-out and push-in tests were carried out on 15·2 mm diameter prestress steel strands sealed in 18 mm diameter holes with several embedment lengths, complemented by long-term tests. Experimental results are presented and compared with theoretical results regarding maximum pull-out and transmittable loads and also draw-in results. Theoretica...
A significant number of existing flat slabs currently require strengthening against punching shear for safety reasons (the increase of applied loads and deficiencies during design or construction) or to comply with more stringent code requirements. Available strengthening methods are, however, not completely satisfactory, or they cannot be applied in many cases (depending on the possibilities to enlarge column sizes or to intervene on the upper face of slabs). In this paper, an innovative system...
Engineering failures get a lot of attention—inciting morbid curiosity and fueling concern over the condition of our infrastructure. But every engineering loss is the start of a forensic investigation into how, why, and what can be done to prevent future failures. As with scientific failures, engineering failures can be very instructive in teaching us what does not work. Beyond Failure presents the circumstances of important failures that have had far-reaching impacts on civil engineering practic...
The progressive collapse of structures generally results in the loss of human lives. Experience shows that flat slab structures are very sensitive to progressive collapse, which may cause serious accidents if special detailing is not provided. The post-punching behaviour of a column-supported slab is decisive in the progressive collapse development. This work presents the experimental research carried out to study the post-punching behaviour of prestressed concrete flat slabs. Six reduced-scale ...
Abstract This paper summarises the report of the committee of inquiry into the collapse, by punching shear, of the Sampoong department store in Seoul, Korea in 1995. It examines the adequacy of the design and calculates, using ACI 318-89, BS 8110-85 and Gardner 96, the contribution of the various deficiencies to the probability of failure. ACI 318 does not predict the collapse but BS 8110 and Gardner 96 predict a large probability of collapse. Both BS 8110 and Gardner 96 include size effect and ...
The paper reports tests designed to study the improvement in the post-punching resistance of slab–column connections by the provision of bottom bars passing through the columns and anchored in the slab. A series of model tests on slabs was used to developan expression for the strength limit governed by the slab concrete, while large-scale tests on abbreviated specimens were used to formulate the criterion dependent on the failure of the reinforcement. It is demonstrated that bottom reinforcement...
Introduction to the model code basis of design material properties general model data for prestressing structural analysis verification of the ultimate limit states verification of serviceability limit states durability detailing limit measures practical construction quality assurance and quality control maintenance precast concrete elements and structures appendices.
The response of slab structures after initial failure is investigated in order to determine a means of preventing progressive collapse. Analytical models for predicting the post‐failure response of slabs are presented and the predictions are compared with experimental results. These analytical models along with an experimental investigation enabled the development of simple design and detailing guidelines for bottom slab reinforcement which is capable of hanging the slab from the columns after i...
#1Youzhe Yang(Beijing University of Technology)H-Index: 1
#2Yi Li(Beijing University of Technology)H-Index: 17
Last. Xinzheng Lu(THU: Tsinghua University)H-Index: 1
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Abstract null null To enhance post-punching strengths and deformation capacities of flat plate-column joints for mitigating progressive collapse, two strengthening methods including stirrups and embedded ring beams within the joint regions were proposed. An experimental test program on six flat plate-column joint specimens with in-plane constraints was conducted under the modes of upward punching shear failure (UPS mode) and downward punching shear failure (DPS mode). The specimens included two ...
Abstract The present study focused on creation of an internal strengthening system, which involved embedding a post-tensioned PC tendon in a wedge-shaped anchorage of an existing concrete member. Under conditions with narrow work spaces, it was difficult to employ the previous system using a post-tensioned prestressing bar, as adequate backspace was required to install the bar. A flexible hollow corrugated pipe covered with steel wire cables seemed applicable even in such narrow spaces. Interest...
Brittle punching failures can occur in slab–column connections due to earthquake-induced unbalanced moments. The performance of undamaged specimens and various repair/strengthening techniqu...
Abstract A new strengthening system, which embeds a post-tensioned PC bar tendon into the wedge-shaped anchorage of an existing concrete member, was developed. Previously, the adequate load-bearing capacity of the prestressing tendon anchorage was confirmed on simple element specimens. In the present study, the developed system is applied to the addition of new concrete members to old concrete structures. The strengthening effect of the system was examined in a loading test on jointed full-scale...
Abstract The present study aims to develop a strengthening system using prestressing tendons embedded into an internal anchorage of concrete member. The internal anchorage, a wedge-shaped hole, is made by using a special drilling machine. The tip of the hole is filled with high strength mortar to anchor firmly the prestressing tendon. The strengthening system is acceptable even in relatively narrow workspaces, and also applicable for joints between existing and additional concrete members. The e...
Last. Thomas Keller(EPFL: École Polytechnique Fédérale de Lausanne)H-Index: 45
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An experimental study of full-scale reinforced concrete flat slabs crosswise strengthened with prestressed carbon fiber-reinforced polymer (CFRP) straps against punching shear was performed. The effects of two strap anchoring systems and of slab thickness on punching behavior were compared. In one system the anchors were adhesively bonded to the concrete surface, while an external steel frame balanced the horizontal strap force components in the second system. Strap activation and thus strap for...
