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Analyse de la rupture par cisaillement des poutres et dalles sans armature d'effort tranchant.

RC slabs without shear reinforcement subjected to c oncentrated loads near lin ear supports are typical cases of deck slabs of bridges, transfer slabs or pile caps. Such elements are often designed or as­ sessed in shear with code provisions calibrated on the basis of tests on one-way slabs or beams with rectangular cross section, even t hough these tests are not representative of the actual behavior of two­ way slabs (non-parallel direction of shear forces and potential shear redistributions). Also the pres­ ence of prestressing ducts and slab inserts may infl uence the shear strength. In addition, the concen­ trated loads of the deck slabs are applied a number of cycles during the service life of the structure and may potentially lead to fatigue problems. In this investigation, two experi mental campaigns are presented. The first one consists of 12 static tests on 6 full-scale slabs subjected to a concentrat ed load with a central line support that allows evaluating the linear reaction. Parameters such as the location of the concentrated loads (3 locations) and presence of ducts (4 types) were varied. Th e second campaign has a sim ilar test setup and con­ sists of 4 static tests on 2 full-scale slabs (reference tests, failure load Q static ) and fatigue testing on 8 other slabs, varying the maximum applied load and the load location (2 locations). So far two slabs failed in shear ( Q max =90% and 80% Q static ) and two others due to bar fracture (fatigue in bending, Q max =70% and 60% Q static ) that ultimately led to shear failures. All slabs that statically failed in shear showed significant shear redist ributions prior to failure. This research aims to study the observed phenome na within the framework of the Critical Shear Crack Theory (CSCT) and to provide more data to the poor existing datasets . Comparisons with the fib- Model Code 2010 are presented. The ultimate goals of the research are to reduce the number of existing structures that need to be strengthened and to provide consistent design methods for new structures and assessment of existing ones.

Most research efforts in the past related to the punching resistance of reinforced concrete slabs have concentrated on the response of internal slab-column connections, where significant advances in the state-of-the-art have been performed. Other than internal connections, edge slab-column connections are also very common cases in flat slabs, with a strength usually governed by punching shear conditions as well. Their response is more complex than those of internal slab-column connections, due to the potential moment transfer from the slab to the column and to the uneven shear and moment fields. However, scanty experimental evidence is available due to the difficulty of testing such system under realistic conditions. As a consequence, knowledge on the phenomena governing failure is still limited and predictions of the strength are in most cases performed by adapting punching shear models for internal slab-column connections. In this paper, the main results of an experimental programme on edge slab-column connections is presented, comprising specimens both with and without shear reinforcement. A novel test setup was developed to effectively introduce the effect of continuity in the direction perpendicular to the free edge of the slab. Moreover, refined measurements were performed by using Digital Image Correlation on the concrete surfaces and Fibre-Optic Measurements in selected flexural reinforcement bars and shear reinforcement, allowing for direct measurements of displacements and strains in the critical regions. Based on the experimental observations, a discussion is held on the mechanics governing punching failures of edge slab-column connections.

This paper presents the results of an experimental test series on the soil-structure-pavement interaction in the vicinity of the transition slab at the end of an integral bridge. The main function of transition slabs is to ease the transition between the bridge deck and the embankment in case of differential settlements. Additionally, in the case of integral bridges, they can solve the problem of moderate imposed longitudinal deformations at the bridge ends. In this case, the displacements imposed to the transition slab can lead to vertical and longitudinal surface displacements and to cracking of the pavement. Based on the observed behaviour, some recommendations are proposed for the geometry and surface conditions to optimise the behaviour of the transition slabs.

Punching shear reinforcement is increasingly used in flat slabs as an effective solution to increase their strength and deformation capacity. Several punching shear reinforcing systems have been developed in the past, such as studs, stirrups or bent-up bars. The efficiency of such systems is strongly influenced by their development conditions (anchorage, bond) and detailing rules. Codes of practice, however, do not typically acknowledge such differences, proposing the same set of design formulas for all systems. This approach is detrimental for some systems (with better detailing rules and anchorage characteristics) and does not provide enough guidance for design of others (not respecting codes’ detailing rules). In this paper, the fundamentals of the critical shear crack theory are explained with respect to the design of punching shear reinforcing systems. It is shown that this theory provides a consistent basis for design of shear reinforcing systems accounting for their particularities and modes of failure. The results of 6 tests on full scale slabs (3.0× 3.0× 0.25 m) with same flexural and shear reinforcing ratio but with different punching shear reinforcing systems are presented and discussed. The experimental results confirm that the strength and deformation capacity are strongly influenced by the characteristics of the shear reinforcing system. The results for the various systems are finally investigated within the frame of the critical shear crack theory, leading to a series of recommendations for design

A reinforcing element (10) for structural concrete construction comprising a rod- shaped bar (1 1 ) having a cross-sectional enlargement on at least one end thereof. The rod shaped member (11 ) comprises an elbow portion (12) on said at least one end being embedded in a protection block (15), thereby forming said enlargement. The method for producing the reinforcing element and the corresponding reinforced structural concrete construction are also provided.

Structural R/C cores are a popular and efficient choice as lateral-load resisting system in medium to tall buildings. The walls of the cores typically present large openings providing access to elevators placed within them. Shear induced by lateral forces has thus to be transmitted by limited portions of the core (wall between openings) which are commonly named coupling beams. Such beams are subjected to large deformation demands as the system undergoes lateral displacements associated to wind or earthquake forces, and typically govern the response of the structural system. Performance-based assessment and design of these members have been gaining popularity within the structural engineering community approximately during the last 15 years. These techniques rely on accurate definitions of component behavior (shear force – chord rotation) for their successful application to overall system performance. In current seismic design and assessment documents, the influence of some instrumental parameters such as slenderness, reinforcement layout or even failure mode is not (or only partly) addressed. In this paper, the influence of these parameters is investigated on the basis of the results of an experimental campaign. Several approaches to generate force-deformation envelope (backbone) curves for coupling beams are discussed and compared. The use of stress field models is introduced as a promising technique to rationally represent the backbone envelope behavior of elements subjected to cyclic loading.

In: SIA D 0160, Progrès dans la conception des ouvrages en béton (1999), p.33- 36

The mechanical model of the critical shear crack theory (CSCT) has been used in the past to investigate a number of shear-related problems, such as punching of slab–column connections with and without transverse reinforcement. In this paper, a discussion on the differences and analogies between slender slabs and squat members (footings) without transverse reinforcement is presented on the basis of the CSCT. This discussion highlights how bending and shear deformations influence the opening of the critical shear crack and eventually its ability to transfer shear forces. On that basis, it is investigated and justified a power-law expression to characterize the failure criterion of the CSCT. This criterion, in combination with a suitable load–deformation relationship, can be used to derive closed-form expressions for punching shear design. The accuracy of these expressions is verified against databases of slender slabs (121 specimens) and footings (34 specimens) with consistent agreement.

This paper presents the theoretical basis and the main results of an analytical model that describes the pre– and post–yield response of bond in reinforced concrete, as well as its influence on the behavior of structural members. The model is based on a number of reasonable assumptions that simplify the differential equation governing the phenomenon. In this way, a closed–form integration is feasible in certain cases, and relatively simple but accurate expressions can be worked out for the interface slip, the strain and the stress in the reinforcement and the bond stress at the bar–concrete interface. Applications are made to different structural members (pull–out specimens, tension ties and beams in bending), whose behavior is well documented in the literature. The agreement between the available test data turns out to be quite satisfactory. Consequently, the proposed model can be usefully adopted for studying the serviceability behavior, the ductility and the post–yield response of a variety of reinforced–concrete members.

Despite the advances on the understanding and modelling of shear and punching shear failures, the application of actual design models to some stations remains still complex. In addition, other significant phenomena such as compressive membrane action and moment redistribution may also develop influencing the shear/punching strength. The procedure is based on nonlinear finite element analysis of RC slabs modelled using mult-layered shell elements. Nonlinear finite element analyses (NLFEA) results obtained using PARC-CL crack model, implemented at the University of Parma in Abaqus Code, are post-processed according to the failure criterion of the Critical Shear Crack Theory (CSCT) to predict the punching shear strength of continuous slabs.

This paper presents some applications of FRC in Switzerland and recent developments resulting from research activities carried out at Swiss university laboratories. The national recommendation SIA162/6 "Steel Fiber Reinforced Concrete" is also briefly presented in relation to the practical use of this material in terms of quality control and design. Finally, some perspectives of the use of FRC in the Swiss market are given.

Cours d'introduction à la norme SIA 262.

Large efforts have been devoted in the past to understanding size effect in shear failures of members without transverse reinforcement. Experimental works have demonstrated that increasing the size reduces the nominal shear strength provided that the failure mode is brittle. For large specimen sizes where a linear behavior can be assumed between the opening of the shear cracks and the acting shear force, the size effect agrees with linear-elastic fracture mechanics (LEFM). In this case, the reduction of nominal shear strength is characterized with respect to the specimen size by an asymptotic slope (in double-log scale) of -1/2. However, such a linear relationship between crack widths and applied shear force is not present in most reinforced concrete structures, where the response is characterized by a nonlinear behavior at a cracked stage. In these cases, the influence of size effect shall be milder, and the slope (in double-log scale) characterizing it shall be lower than -1/2. In this paper, the influence of size effect on structures characterized by internal redundancy (continuous one-way members and slabs in case of punching shear with a nonlinear response) is investigated in the frame of the critical shear crack theory. The theory predicts the same influence as LEFM with respect to size effect when a linear behavior can be assumed, but it yields consistently milder influence of size effect for structurally redundant elements with a nonlinear response.

This paper presents the results of six tests on R/C bridge cantilever slabs without shear reinforcement subjected to concentrated loading. The specimens represent actual deck slabs of box-girder bridges scaled 3/4. They were 10mlong with a clear cantilever equal to 2.78mand with variable thickness (190mm at the tip of the cantilever and 380 mm at the clamped edge). Reinforcement ratios for the specimens were equal to 0.78% and 0.60%. All tests failed in a brittle manner by development of a shear failure surface around the concentrated loads. The experimental results are investigated on the basis of linear elastic shear fields for the various tests. Taking advantage of the experimental and numerical results, practical recommendations for estimating the shear strength of R/C bridge cantilever slabs are proposed.

The fib Model Code 2010 (MC2010) contains a semi-empirical formulation for the local bond-slip relationship for both pull-out and splitting failure modes (derived from short pull-out tests), as well as a semi-empirical formulation of the steel stress that can be activated in the reinforcement as a function of the anchorage length (anchorage resistance derived from a large database of lapped joint and anchorage tests). Considering equilibrium and compatibility conditions, the anchorage strength can be calculated on the basis of the local bond-slip relationship. Using this approach with the bond-slip relationship of MC2010, the obtained anchorage strengths are not consistent with the anchorage resistance according to the same code. Recent works have shown discrepancies between measured local bond-slip responses and the proposal of MC2010. Within this frame, this paper presents an experimental programme consisting of pull-out tests instrumented with detailed measurement systems (digital image correlation and fibre-optic measurements). The results show the effect of the evaluated parameters in the local bond-slip relationship along the bar. The different local bond-slip responses can be explained by the crack development in the surrounding concrete.

the bridges over the river Capriasca (1996) and over the river Ticino (1997) are characterised by the application of an innovative structural system. The central part of the main span of both bridges is constituted by the bridge concrete deck with two longitudinal stiffening girders, constituted by polygonal steel members that contain two prestressing tendons each.

Le prescrizioni inerenti il punzonamento di colonne attraverso piastre in calcestruzzo armato e fondazioni secondo SIA 262/2003 [1] sono uno sviluppo del metodo di verifica secondo SIA 162/1993 che si basa su studi teorici [2,3]. I principi di questo metodo e le novità rispetto alla norma precedente sono stati descritti nel corso di introduzione [4] e sono in parte integrati in questo testo. Nuovi risultati di ricerche [5] ed esperienze raccolte durante le perizie negli ultimi anni ci permettono di completare il testo citato [4] con commenti e nuovi risultati sia pratici che teorici. Questo contributo è di responsabilità esclusiva degli autori e non della Commissione per la norma SIA 262 Costruzioni in calcestruzzo.

On April 2010, the first complete draft of new Model Code 2010 was published. It introduced a number of innovative design approaches, some of them with respect to shear and punching shear. Contrary to Model Code 90 (or some national and international codes such as ACI 318-08, EC-2 or EHE-08), the new Model Code 2010 grounds such design approaches on physical models rather than on empirical formulas. This paper gives an overview of the methodology proposed for punching shear, which is based on the critical shear crack theory. The fundamentals of this theory are explained and justified as well as the application of the theory to the design and assessment of flat slabs. The paper also introduces the design of structures following a levels-of-approximation approach and how can this be applied to punching shear design.

In Switzerland, the current code for structural concrete published in 2003 privileged an incremental approach for design of new members or for assessment of existing structures with respect to a number of topics (shear, buckling, reinforcement detailing through strut-and-tie modelling,...). The incremental approach is grounded on the use of general and sound theories (based on physical models) where the hypotheses performed for their application can be refined as the required accuracy increases. The approach proposes thus to adopt safe hypotheses at first stages of design leading to relatively simple and low time-consuming analyses. In cases where such degree of accuracy is not sufficient, the hypotheses are refined in a number of steps, leading to better estimates of the behaviour and strength of the member. Such approach has revealed to be very convenient for design of new structures (where different levels of detail are required as the project evolves from preliminary or conceptual design to a construction project) or for assessment of existing structures, where the structural safety may be found insufficient according to simple design rules.

Le projet de recherche Evaluation des systèmes existants pour le suivi à long terme des déformations des ponts a été initié dans le but de préparer sous forme condensée une présentation et une évaluation des systèmes de mesure existants pour le suivi à long terme des déformations de ponts ainsi que des recommandations en vue d’applications particulières. Ce sujet est d’actualité car d’une part il importe de gérer au mieux les ouvrages et les ressources et d’autre part parce que plusieurs cas de déformations importantes de ponts en béton précontraint ont été constatés tant en Suisse qu’à l’étranger ces vingt dernières années. Ce document est premièrement destiné aux maîtres d’ouvrage pour les assister dans le choix des méthodes applicables aux ouvrages dont ils désirent suivre l’évolution et l’organisation des campagnes de mesure. Il doit permettre une utilisation rationnelle des moyens et des méthodes de suivi à long terme des ouvrages. La majorité des méthodes de mesures répertoriées sont bien connues. Le présent document définit leur domaine d’application et leurs limites. Certaines méthodes sont plus récentes et moins connues. Leurs propriétés et leur domaine d’application sont cernés et comparés à ceux des méthodes classiques. Il faut noter que plusieurs domaines de mesure qui ont été investigués sont en période de profonds changements, avec une intégration de plus en plus intime entre diverses méthodes de mesure, rendue possible par l’émergence de nouvelles techniques (positionnement GPS par exemple) et par l’intégration de l’informatique dans une grande partie des opérations de mesure. Il est probable qu’une ou plusieurs des méthodes de mesure nouvelles qui ne sont à l’heure actuelle pas encore mûres pour une application de terrain atteindront ce stade dans les années qui viennent. Il serait souhaitable d’accompagner et d’encourager leur développement par la mise sur pied de projets-pilotes de suivi des déformations. The research project Evaluation of existing measurement systems for the long-term monitoring of bridge deflections was initiated with the aim to prepare, in a condensed form, a presentation and comparison of the existing measurement systems for the long-term monitoring of bridge deflections, as well as recommendations for special applications. This is a very actual topic, as on the one hand, it is necessary to efficiently manage existing bridges, and on the other hand because several cases of large deflections of post-tensioned concrete bridges have been observed in Switzerland and other countries over the past 20 years. This document is primarily aimed at bridge owners to assist them in the selection of applicable methods to monitor bridges and to organise measurement campaigns. It will facilitate a rational use of available means and methods for the long-term monitoring of bridges. The majority of measurement methods listed are well known. The present document defines their application domain and their limitations. Some methods are more recent and less well known. Their properties and application domain are outlined and compared to those of classical methods. It must be noted that several of the measurement domains investigated are presently undergoing a period of profound changes, with increasingly more intimate interactions between various measurement methods. This convergence is made possible by the emergence of new measurement techniques (GPS positioning for example) and by the integration of computers in a large part of measurement methods. It is likely that one or more of the new measurement methods that are currently nor ready for field development will mature in the coming years. It would be advisable to follow and encourage their development through pilot projects of deflection monitoring.

Over the past century, the use of flat slabs in buildings and especially in parking garages has been growing as it is an economic and efficient solution. Flat slabs are easy to build and have, through their smaller depth, an economical and architectural advantage compared to slabs on girders. Because of their limited depth, flat slabs are especially sensitive to deflections and to punching shear, which are their main design criteria. Furthermore, flat slabs without punching shear reinforcement have a rather brittle failure mode with little deformation capacity. This behavior potentially limits the redistribution of the internal forces in flat slabs in the case of punching of an isolated column and can thus lead to progressive collapse of the entire structure. To increase both the strength and the deformation capacity of flat slabs, punching shear reinforcement can be provided in the vicinity of the columns. Although the influence of punching shear reinforcement on the strength of flat slabs has been intensively investigated, there are still fundamental uncertainties such as the contribution of the shear reinforcement and the strength of the concrete struts close to the column. The paper presents the results of an extensive experimental campaign performed at the Ecole Polytechnique Fédérale de Lausanne (EPFL). Sixteen full-scale slab specimens (3.0 x 3.0 m in plane) with varying parameters such as the column size, the slab thickness, the shear reinforcement ratio, and the shear reinforcing system have been investigated. The performance of these specimens is analyzed and compared to modern design codes and to the critical shear crack theory.

Ce polycopié constitue le document de référence du cours "Structures en béton" dédié aux étudiants du 5ème semestre de la section Génie Civil de l'Ecole Polytechnique Fédérale de Lausanne.

Physical punching shear models such as the Critical Shear Crack Theory (CSCT), which is the basis of Model Code 2010 (MC 2010), describe generally the punching strength as a function of the slab deformation. Thus, the prediction of an accurate load-deformation curve is essential for the prediction of the punching strength as well as the deformation capacity of flat slabs. In the vicinity of columns, the flexural response of flat slabs depends not only on the flexural moments but also on the concentrated shear forces. In the case of slender slabs, slabs with low amounts of flexural reinforcement, or slabs without shear reinforcement, the shear forces are limited and thus their influence in the flexural response is low. However, in the case of thick slabs with shear reinforcement, large shear forces are carried influencing the flexural response of the flat slab. Despite the importance of an accurate prediction of the load-rotation response, little research has yet been performed on this subject. This paper presents an investigation on the flexural response of 6 full-scale flat slab specimens. The specimens presented herein belong to an extensive experimental campaign of 16 full-scale flat slab specimens performed at the Ecole Polytechnique Fédérale de Lausanne (Switzerland) with the aim to investigate the punching strength and the rotation capacity of flat slabs with and without shear reinforcement. The investigated parameters were the column size, the slab thickness, the amount of shear reinforcement, and the type of shear reinforcement system. The investigation of the flexural response consists of the comparison of the experimentally obtained load-rotation responses to the predictions by the CSCT, MC 2010, and a modified approach based on the CSCT.

The authors report on punching tests with full-scale slab specimens. The objective was to investigate the influence of several parameters on the punching strength and rotation capacity of flat slabs

Code design of slab-column connections to resist seismically induced drifts is currently based on empirical relationships for both moment and deformation capacity. The results of tests on slab-column connections are however sensitive to the conception of the test setup. This paper presents a new setup configuration as well as first results of an experimental campaign carried out at EPFL. Within this campaign slabs without shear reinforcement will be subjected to constant vertical loads and increasing seismic moments. Parameters investigated are the vertical loads, the longitudinal reinforcement content of the slabs, the column size and the loading history (monotonic vs. cyclic). Results of the first three out of sixteen tests showed that the drift capacity of relatively thick slabs is smaller when compared to thinner ones tested by other researchers [7]. The influence of the gravity induced shear force on the seismic moment and deformation capacity of the connections is found to be well pronounced. A comparison of a monotonic and cyclic test for high vertical loads showed that the deformation capacity of the cyclically loaded slab is smaller than of the monotonically loaded one.