Aurelio Muttoni

Swiss Federal Institute of Technology in Lausanne | EPFL · Civil Engineering Institute

Reinforcing bars in structural concrete are typically designed to carry axial forces. Nevertheless, due to their bending stiffness, the bars can also carry transverse forces, that are associated with the localized bending mechanism (dowel action) resulting from the relative displacements (or slip) wherever a crack interface or a discontinuity inter...

Estimating the stress of reinforcing bars and its variations in service conditions can be useful to determine the reserve capacity of structures or to assess the risk of fatigue in the reinforcement. This paper investigates the use crack width measurements to estimate the stress in the bars. In existing structures, crack width formulations can be u...

In typical reinforced concrete design, reinforcement is designed to carry axial forces, but it can also resist transversal forces by dowel action. This is usually neglected for simplicity's sake in the design phase, but it can be accounted for either explicitly in mechanical models or implicitly in empirical relationships. Furthermore, there are ca...

For the dimensioning and assessment of structures, it is common practice to compare action effects with sectional resistances. Extensive studies have been performed to quantify the model uncertainty on the resistance side. However, for statically indeterminate systems, the model uncertainty in the calculation of action effects has not been properly...

The use of steel fibre reinforced concrete (SFRC) is a well-known method for enhancing the punching and flexural resistances of flat slabs. The structural performance of SFRC elements depends significantly on the fibre distribution and orientation, which are typically unknown. One of the largest uncertainties regarding the performance and reliabili...

Desde los inicios del hormigón estructural hasta la fecha se han dedicado muchos esfuerzos de investigación a la cuestión del diseño a cortante de elementos sin armadura transversal. Esto ha permitido una serie de avances notables en la comprensión del fenómeno, que en la actualidad se admite como dependiente de un número de mecanismos de transfere...

Shear design and verification of bridge deck slabs subjected to concentrated loads (as those of wheels from traffic) is a topic subjected to scientific and engineering debate, where several questions remain open. Several design procedures have been proposed in the past to determine suitable values of the internal forces for design, such as the so-c...

Rebar‐to‐concrete bond is a fundamental aspect of the behavior of reinforced concrete structures. The characterization of the interface response is challenging due to the complexity of the physical phenomena and the large number of factors involved. Locally, the response is characterized by the bond–slip relationship, which is typically obtained ex...

Many of the existing reinforced and prestressed concrete infrastructures, such as bridges, subways or overpasses have reached or will reach, in this decade, half a century of existence, making it timely to assess their structural safety accounting for their state. It is desirable that the assessment of existing structures is carried out following a...

As an outcome of a recent European research project, the modelling of the response of flat slab structures for seismic and cyclic loading was the object of a blind competition. No other blind tests are available in the literature on this topic. The test results concern a full-scale, two-storey, three-by two bay reinforced concrete flat slab frame....

The Critical Shear Crack Theory (CSCT) has been developed since 1985 to assess the shear resistance of members without shear reinforcement and the punching shear resistance of reinforced concrete slabs in a rational manner. The main idea of the CSCT is that the shear resistance is governed by the development of a critical shear crack, its geometry...

Due to the significant shear forces developing around columns and the potential brittle failure associated, the punching capacity of flat slabs is the main concern at ultimate limit state. An effective way to understand the behaviour of slab-column connections has typically been by testing isolated specimens in the laboratory. While there exist man...

The Serviceability Limit States (SLS) of reinforced concrete structures, where cracking and deflection limits are verified in the design process, are directly related to time-dependent properties of concrete. In this study, the effects of creep and shrinkage of concrete, implemented in a Finite Element Model for Non-Linear Analysis, are in-deeply i...

Openings in flat slabs near to columns are often needed to supply the building with utilities. The presence of these openings can lead to a decrease of the punching resistance which is related to (i) the reduction of the control perimeter, (ii) the stress concentrations at the edges of the openings, (iii) the reduction of the unitary shear resistan...

The minimum amount of shear reinforcement to be provided in reinforced concrete members has been a topic of debate and research for decades without reaching a consensus. Defining such values is however instrumental to build in an economic manner and to safely ensure the applicability of the models used for design or assessment. This paper presents...

As acknowledged explicitly or implicitly in most of current design codes, a high level of sustained loading has a detrimental effect on the concrete compressive strength. However, its beneficial effect in terms of deformation capacity is neglected in most cases. This latter topic and its practical consequences are addressed in the present paper on...

Within the frame of the revision of the Eurocode 2 for concrete structures, the section devoted to strut-and-tie design has been updated to enhance its applicability, its consistency with other sections and its ease-of-use. As a result, a number of changes have been introduced. Namely, the use of stress fields and their combination with classical s...

The revision of a code is a long-term project that shall fulfil several aims, comprising the enhancement of the ease-of-use and incorporating updated state-of-the-art. With respect to the revision of Eurocode 2 concerning the punching shear provisions, this task allowed also for the opportunity to enhance the understanding of the code and physical...

As proposed in several design standards for structural concrete, including Eurocode 2 (EN:1992‐1‐1:2004) and fib's Model Code 2010, the shear design of slender members with shear reinforcement can be performed by means of consistent models based on suitable stress fields. This is for instance the case of the variable‐angle truss models, where the a...

Crack formation and development in reinforced concrete structures is a complex mechanism affected by a large number of factors. Typically, the estimation of the crack width as a function of the reinforcement stress state is based on simplified assumptions concerning the rebar-to-concrete interaction. In this paper, the results of concrete ties and...

Strengthening of flat slab-column connections to resist imposed lateral drifts is often required for older reinforced concrete structures in which the flat slabs were typically designed to resist gravity load only or have been designed for less stringent requirements. The complex stress state around the columns means that strong experimental eviden...

The fib Model Code offers pre-normative guidance based on the synthesis of international research, industry and engineering expertise. Its new edition (draft MC 2020) will bring together coherent knowledge and experience for both the design of new concrete structures and the assessment of existing concrete structures. This contribution presents an...

The increasing usage of nonlinear analyses for the design of reinforced concrete structures and the necessity of codes of practice to provide a consistent safety format for them is one of the challenges that new generations of codes of practice are facing. Suitable safety formats shall thus account for the peculiarities of nonlinear analysis, such...

Anchorage of shear reinforcement, such as links or stirrups, can be performed by providing hooks, bends or heads at their ends, by welding transverse reinforcement or by closing open stirrups with pins. Hooks and bends, also used to enhance the anchorage of flexural reinforcement at the end regions of beams and slabs, have often been preferred beca...

The fib Model Code 2010 (MC2010) contains a semi-empirical formulation for the local bondslip 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 resistan...

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...

The load-carrying capacity of many reinforced concrete structures is governed by shear failures, occurring before reaching the flexural capacity of the member. For redundant systems, such as slabs subjected to concentrated loads, local shear failures (typically initiated at locations with highest shear forces) can however occur after redistribution...

In flat-slab frames, which are typically designed as secondary seismic structures, the shear failure of the slab around the column (punching failure) is typically the governing failure mode which limits the deformation capacity and can potentially lead to a progressive collapse of the structure. Existing rules to predict the capacity of flat slab f...

Design and verification of structures in modern codes of practice account for a safety format, ensuring that the probability of failure does not exceed a given threshold. Although specific safety formats are proposed in some cases for special types of structures or analyses, most designs and verifications are currently performed on the basis of the...

Plastic bending of reinforcement bars against mandrels is the usual procedure to provide bends and hooks for steel reinforcement bars. Minimum mandrel diameters are usually given in to codes of practice, depending on the type of detail and diameter of the bar. These recommendations for the bend diameter ensure a safe transfer of forces, avoiding sp...

Full-scale testing of a two-storey flat slab structure is reported, undertaken in the SlabSTRESS research project; the construction and testing were planned and carried out at the ELSA laboratory of the European Commission's Joint Research Centre. The dimensions are three bays by two, spans 4.5 and 5 m, slab thickness 0.2 m, interstorey height 3.2...

The paper presents a proposal for the structural preservation of the Basento Bridge in Potenza (1967-1975), designed by the engineer Sergio Musmeci (1926-1981) and regarded as one of the most relevant examples of 20 th century reinforced concrete infrastructures in Italy. The geometry of the Basento Bridge, which is the most characteristic feature...

Design of slab-column connections in flat slabs is typically governed by punching resistance at ultimate limit state. This failure mode has attracted numerous research efforts in the last decades in an effort to produce consistent design provisions and to overcome empirical design formulations traditionally adopted in codes of practice. From these...

This paper investigates the phenomenon of cover spalling in reinforced concrete induced by bond or by the action of an inner pressure. This research is based on an experimental programme comprising a series of bond tests and a series of tests with inner-pressure on cylindrical openings. The inner-pressure test series (aimed at representing the cond...

The use of punching shear reinforcement is currently considered as one of the most convenient practices to enhance the punching shear strength and deformation capacity of slab-column connections in flat slabs. Intensive research has been performed in the last decades on this topic, evidencing the complexity of the phenomenon, which is dependent on...

Redistribution of shear forces in reinforced concrete members without shear reinforcement is a key aspect for the assessment of the shear capacity of wide beams and slabs. Such redistributions are due to the nonlinear response of reinforced concrete (both in bending and shear) and have the potential to significantly modify the internal forces durin...

The phenomena associated with the consolidation of fresh concrete (bleeding and plastic settlement) are commonly considered significant for the bond performance of reinforcement. However, rules to take care of such influence for design are not consistent amongst design recommendations and may lead to notable differences. With this respect, two fail...

The bond response of deformed bars in structural concrete is a phenomenon governed, to a large extent, by the rib-to-concrete contact and interaction, with contact forces depending on both material properties and the kinematics between the contact surfaces (slip and potential separation between the bar and concrete). This phenomenon, presenting sim...

Aggregate interlocking is acknowledged as one of the most significant actions transferring shear forces in cracked concrete structures and has been investigated for several decades. Despite the many experimental programmes and previous efforts to develop models based on mechanical approaches, a number of instrumental issues of the phenomenon are st...

Simplified assumptions have traditionally been made on the rebar–to–concrete interaction in structural concrete to calculate the stress state in rebars. Such assumptions typically consider a uniform stress state in the reinforcement at a given cross section, neglecting compatibility of deformations due to bending of the bar. Such simplifications ar...

Textile Reinforced Concrete (TRC) is a cementitious composite material where a carbon or glass fabric is embedded as reinforcement. The use of TRC allows building thin and light structures, with reduced concrete covers and an enhanced durability due to the absence of corrosion problems. In this article, the response of TRC elements subjected to ten...

Flat slab buildings for commercial, office and residential use are built in many countries. Yet, their behaviour under seismic and gravity actions is still not very well understood. Many studies have been carried out in North America but European research is lagging behind and currently Eurocode 8 does not cover the design of buildings with flat sl...

Textile Reinforced Concrete (TRC) is emerging as a promising alternative to ordinary Reinforced Concrete for the construction of durable, lightweight and more sustainable structures, with a large potential particularly in shells and thin members. Research on the response of TRC in bending and shear as so far been performed on the basis of different...

The compressive resistance of concrete in new structures is usually characterized on the basis of tests performed on concrete cylinders or cubes under relatively rapid loading conditions. Although efficient for material characterization, these tests do not acknowledge a number of phenomena potentially influencing the compressive resistance of concr...

It is well known that control specimens used to assess the concrete strength of new structures have different casting and curing conditions than those of actual structures. Notably, after pouring of the concrete and before its hardening, a number of phenomena such as concrete bleeding and plastic settlement occur, influencing the in‐situ strength w...

Textile reinforced concrete (TRC) is a cementitious‐based material where reinforcement consists of high‐strength noncorrosive textile fabrics. Due to the use of a noncorrosive reinforcement, cover requirements can be limited to minimum static values and the amount of clinker in the cement can also be notably reduced. In addition, the simplicity to...

Aggregate interlocking allows transferring shear and normal stresses through open cracks, and is considered to significantly contribute to the force transfer in cracked concrete. The complex phenomenon depends on the roughness of cracked surfaces, where material protruding from one side may engage with the opposite one. Two-Phase models were establ...

This paper presents a critical review of the state of the art of experimental research concerning the seismic response of reinforced concrete flat slab frames. After a summary of tests on connections, the paper examines tests carried out on frames with gravity and cyclic lateral loading, and shake table tests; scaled specimens and one real scale st...

Over the past two decades, a substantial amount of research has investigated the effects of thermal loads associated with the geothermal operation of energy piles on their mechanical response. Based on this research, consensus about the need for considering the effects of thermal loads on the geotechnical and structural design of energy piles has b...

Many research efforts have so far been devoted to the topic of shear design of members without transverse reinforcement since the first development in structural concrete. This has allowed a number of significant advances in the understanding of the phenomenon, which is currently acknowledged to depend upon a number of shear‐transfer actions in cra...

The detrimental influence of high levels of sustained load on the compressive strength of concrete has been acknowledged and investigated since the 1950s. Despite the potential significance of this phenomenon in many situations, current design codes still provide limited guidance on how to account for this effect at ultimate limit state. In additio...

This document is a reply to arXiv:1810.11506. In that document, D\"onmez and Ba\v{z}ant raise a number of criticism on the hypotheses Critical Shear Crack Theory (CSCT). The aspects criticized have however been largely discussed in previous works of the CSCT, proving the validity of the theory. This document compiles such previous knowledge as a re...

The design of reinforced concrete flat slabs can be governed at failure by punching shear close to concentrated loads or columns. Geometrical features, reinforcement layouts and in-plane forces provided by external vertical elements, such as shear walls, can affect the membrane action and, consequently, the punching shear resistance. This paper pre...

Punching shear resistance formulations provided by codes are usually calibrated on test results of isolated specimens that typically simulate the slab zone within the points of contraflexure around the column (hogging area). However, the behaviour of actual continuous flat slabs can be different to that of isolated specimens owing to the beneficial...

This paper investigates the behaviour of concrete failing under high stress levels and subjected to different types of loading. The aim of this investigation is to clarify the development of linear and nonlinear creep strains and how they relate to material damage and eventual failure. This research is supported on the results of a new experimental...

The punching shear resistance formulation provided by Model Code 2010 is calibrated on the basis of experimental tests on isolated slabs supported on columns. According to Level of Approximation approach, several quantities are required for the design punching shear resistance assessment, like the resisting moment and the radius of the line of mome...

A mechanical model is presented for predicting the momentrotation relationship of interior slab-column connections without transverse reinforcement when subjected to seismically induced drifts. The model accounts explicitly for the three load-transfer actions between slab and column contributing to the unbalanced moment resistance - that is, eccent...

In this paper, a mechanical model consistent with the main assumptions of the Critical Shear Crack Theory (CSCT) is proposed for shear design of slender concrete members without shear reinforcement. To that aim, the shear force that can be transferred through the critical shear crack by aggregate interlock, residual tensile strength and dowelling a...

Despite the intensive efforts dedicated in the last decades to better understanding punching shear failures, there is still no consensus on the mechanics governing this phenomenon and on how to implement it within a physical approach. In this paper, an analysis of recent detailed measurements on the kinematics and crack development associated with...

This paper presents an investigation into the ultimate behavior of a recently developed design for keyed shear connections. The influence of the key depth on the failure mode and ductility of the connection has been studied by push-off tests. The tests showed that connections with larger key indentations failed by complete key cut-off. In contrast,...

A large number of design approaches for structural concrete rely on the applicability of limit analysis. This is for instance the case of bending and shear design in members with transverse reinforcement, where it is assumed that plastic compression fields develop in the concrete. The behaviour of concrete in compression, however, cannot be directl...

Aggregate interlock is one of the most significant stress transfer actions in cracked concrete and its understanding is fundamental in order to predict the strength of many concrete structures, particularly members failing in shear. Several test programmes focusing on aggregate interlock have been reported in the literature. These programmes, howev...

Advancing the knowledge about the punching behaviour of flat slabs has been held back by the fact that only indirect measurements of the internal failure mechanism have typically been available. In this paper, a novel experimental approach for tracking the formation and development of cracks inside punching test specimens is presented. In six full-...

A traditional difficulty in the understanding of the role of the various shear-transfer actions in members without transverse reinforcement has been a lack of detailed measurements on the development of shear cracking and their associated kinematics during the process of failure. In this paper, this issue is addressed on the basis of an experimenta...

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 tra...

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 th...

Reinforced concrete (RC) flat slabs supported on columns are one of the most widely used structural systems for office and industrial buildings. In regions of medium to high seismic risk RC walls are typically added as lateral force resisting system and to increase the lateral stiffness and strength. Although slab-column connections possess low sti...

The design of reinforced concrete flat slabs in practice can be governed at failure by punching shear close to concentrated loads or columns. Punching shear resistance formulations provided by codes are calibrated on the basis of experimental tests on isolated slabs supported on columns in axisymmetric conditions. Nevertheless, the behavior of flat...

Reinforced concrete flat slabs supported by slender columns are often used as gravity load resisting system for buildings in regions of moderate seismicity. Current codes of practice determine the displacement capacity of slab-column connections using empirical formulas which were calibrated against experimental studies. This article reviews and co...

The performance of 11 different shear reinforcement systems against punching of inner slab-column connections under gravity loading was compared on the basis of experiments on 12 full-scale specimens, eight of them newly reported. The slab geometry and flexural reinforcement ratio (1.5) were kept constant. The shear reinforcement systems included d...

Provisions for punching shear design of reinforced concrete slabs are usually calibrated on the basis of results from tests on isolated specimens that simulate the slab zone within the points of contraflexure around a column. However, the punching behavior of interior slab-column connections in actual continuous slabs without transverse reinforceme...

Isolated footings are reinforced concrete elements whose flexural and punching shear strengths are usually governing for their design. In this work, both failure modes and their interaction are investigated by means of the kinematical theorem of limit analysis. Previous works in this domain have traditionally considered failure mechanisms based on...

Most classic investigations on bonding properties in reinforced concrete have been performed on the basis of pull-out tests, where a reinforcement bar is pulled out from an uncracked concrete cylinder, prism or cube. In these tests, the bond is governed by the concrete strength and bar surface properties of the reinforcement (bond index, rib geomet...

Punching shear is usually the governing failure criterion for the selection of the depth of reinforced concrete footings. Despite the fact that large experimental programmes have been performed in the past aimed at the punching strength of slender flat slabs, only a few experimental campaigns on full-scale compact reinforced concrete footings can b...

This paper presents the results of a systematic experimental campaign consisting of 13 symmetric punching tests on interior slab-column connections. The study focuses on the influence of varying the size of the supported area and the slenderness of the slab. Other investigated parameters are the flexural reinforcement ratio and the presence of shea...