Coffrage | EPFL Graph Search

thumb|Coffrage Cadres. Le coffrage est une enceinte provisoire, un moule, destinée à maintenir en place un matériau de construction le temps que celui-ci devienne autoportant, soit par prise, séchage (béton, pisé), soit par d'autres contraintes physiques (pierres, dans le cas d'une voûte). Le coffrage a pour but de réaliser des ouvrages aux formes définies par la surface interne du coffrage. Rôles du coffrage vignette|upright=1.5|Coffrages d'angle pour couler des murs à angle droit. Un coffrage est d'usage généralement temporaire, servant au maintien du matériau, depuis le moment de sa mise en œuvre jusqu'à sa prise, à lui donner la forme souhaitée et éventuellement à assurer son état final de surface. Choix du coffrage Les éléments à prendre en compte pour le choix d'un type de coffrage sont :

L'économie : compromis pérennité/amortissement (Représente 40 à 60 % du prix du BA)
L'adaptation aux formes prévues et la modularité
La facilité de mise en œuvre

A Contribution to the Design of Textile Reinforced Concrete Structures

Patrick Lorenzo Valeri

The reduction of green-house gas emissions is one of the global challenges that our society is facing and the production of cement plays a major role because concrete is the most used material worldwide. For every 1000 kg of cement produced, 900 kg of CO2, are released in the atmosphere. In addition, for structural concrete, the generous concrete cover, prescribed by current codes of practice, yields to robust but also to relatively heavy and massive members. Textile Reinforced Concrete (TRC) is a novel building material made of high-strength fabrics embedded in a fine grained mortar matrix. The implementation of non-corrosive reinforcement materials allows to reduce drastically the concrete cover requirements. That empowers to cast extremely thin-walled structural elements and to reduce the structural dead-load up to 90 % (with respect to conventional Reinforced Concrete). In addition to substantial material savings associated to the structure and its foundations, low-clinker-content cements can be used, since no passivation of the reinforcement is required. That, reduces further the environmental footprint and allows to build more sustainable load-bearing structures. Despite its advantages, TRC is hardly implemented in current engineering practice. On one hand there is a lack of design regulations, but on the other, there is also a shortage of construction experiences. With the aim to promote the widespread of TRC, this work addresses both hurdles at three different levels of analysis: First, the tensile response of TRC is investigated by means of an extensive experimental programme. It includes, tests on bare fabrics, the plain mortar and composite tension ties. On the basis of the experimental observations and the coaxial ring analogy, a mechanical model has been derived, allowing to predict the deformation capacity and resistance in a unified manner. That is fundamental to understand the effects of fabric-coating, impregnation, tie- and load introduction length on the load-bearing behavior at a micro-level. More complex loading conditions have been investigated at a meso-scale. Full-scale load tests of thin-walled flanged members have been instrumented with external photogrammetric measurements. These have allowed to validate and adapt the Elastic-Cracked-Stress-Field approach for TRC linear members. The method allows to model beam- and discontinuity regions in a comprehensive manner as well as predicting the response under serviceability conditions and at failure in a unified way, while accounting for both, bending and shear. Finally, the application potential of TRC is addressed at a macro-level. Starting from previous ferrocement works, different formworking materials, casting methods and connections of thin walled members have been explored. The obtained results have been condensed to design, build and erect a full-scale, demountable, prototype pavilion within a three-weeks workshop. Eventually, a proper architectural language has been derived for light-weight structures made of thin-walled TRC members. The structural design can be performed in a comprehensive manner with the Elastic-Cracked-Stress-Field approach, while the resistance of the composite can be estimated with the coaxial ring model. That contributes to the development of code-like prescriptions for TRC and its future implementation in common construction practice for sustainable structures.

EPFL2020

New perspectives for design of lightweight structures by using textile reinforced concrete

Miguel Fernández Ruiz, Aurelio Muttoni, Patrick Lorenzo Valeri

Nowadays, reinforced concrete (RC) is one of the most widely spread construction materials: allowing to build robust and durable structures. Traditionally, due to cover requirements of the reinforcement and to casting and vibration needs, it has yet been associated with heavy and massive structural elements. One possible way to reduce this shortcoming has been identified as to replace steel reinforcement with non-corrosive textile fabrics. This approach known as Textile Reinforced Concrete (TRC), allows to build robust thin-walled structures. Despite the wide spectrum of commercially available fabrics, TRC is not yet a common building solution, due to a large extent, the lack of design provisions and construction experience. In this article both topics are addressed with the aim to increase the level of knowledge on this material. First, a performance-based comparison between several fabrics is made from a material and structural point of view. Second, some construction examples of thin-walled, curved and folded precast prototypes are presented. Finally, formworking techniques and mould materials for such types of elements are discussed.

2019

Equivalency points: Predicting concrete compressive strength evolution in three days

Karen Scrivener, Ian Smith, Marco Viviani

Knowledge of the compressive strength evolution of concrete is critical for activities such as stripping formwork, construction scheduling and pre-stressing operations. Although there are several procedures for predicting concrete compressive strength, reliable methodologies involve either extensive testing or voluminous databases. This paper presents a simple and efficient procedure to predict concrete strength evolution. The procedure uses an experimentally-determined parameter called the Equivalency Point as an indicator of equivalent degree of reaction. Equivalency Points are based on early age concrete deformation and temperature variations. Test results from specimens made from seven concrete types validate the approach. © 2008 Elsevier Ltd. All rights reserved.

Elsevier2008

A Contribution to the Design of Textile Reinforced Concrete Structures

Patrick Lorenzo Valeri

EPFL2020