RC U-shaped walls subjected to in-plane, diagonal, and torsional loading: New experimental findings

Although reinforced concrete U-shaped walls are popular in construction practice internationally, there is a paucity of experimental research investigating the seismic performance of such salient elements. The present paper summarizes an experimental campaign on two slender U-shaped reinforced concrete walls detailed with a single-layer of reinforcement. State-of-the-art instrumentation was used to capture the three-dimensional displacement field of the wall surfaces using digital image correlation techniques. Experimental findings are presented, including strain profiles, equivalent plastic hinge lengths, longitudinal strains at the base, cracking distributions and widths, and out-of-plane deformations. Approximately half of the yielding zone length was found to be equal to the equivalent plastic hinge lengths, which were found to decrease as a function of drift. The longitudinal strains at the base of these walls showed some shear lag effects when subjected to in-plane or diagonal loading. For most directions of loading, the largest crack widths were found to be associated with flexural-shear or shear cracks. When subjected to a pure torque, the vertical strain distribution at the base of the wall correlated with the theoretical distribution for an open section governed by warping torsion. The out-of plane deformations were primarily concentrated within a small region towards the ends of the flanges prior to the local buckling failures that were observed experimentally.

Monitoring and modelling of construction materials during hardening

Marco Viviani

During the past decade, the science of concrete behavior has made much progress and many useful results are now incorporated in technical codes such as those governing mix design, quality of mix and post pouring verification. The stage of Very Early Age (VEA) concrete begins with pouring and ends with hardening. Behavior at this stage influences safety and durability of structures. Concrete is a cast-in-place hardening material. Other hardening materials, such as epoxy mortars have recently raised interest. Techniques used for concrete can potentially be applied to these new composite materials. The overall objective of this thesis is to develop a methodology for predicting mechanical properties and for separating important phenomenon in hardening materials, such as commercial concrete and mortar, to be ultimately applied in real time and in situ. A literature survey has shown a lack of knowledge in the areas of measurement techniques at VEA, prediction of compressive strength, separation of the autogenous deformation and values for the thermal expansion coefficient. This lack of knowledge is especially clear for cement-based materials hardening at varying temperatures. Few VEA data are available and few tools are capable of monitoring VEA parameters. A new device has been constructed to monitor deformations and help identify phenomenological contributions to the total deformation. The design of this device takes into account aspects such as usability in the field and reliability in practice. More than 80 embedded fiber optic sensors and 100 specimens were used for development and testing. Several special sensors have been designed and tested so that their features are adapted to the characteristics of the hardening material at VEA. An important part of this work has been the development of procedures where VEA data are interpreted and reduced in order to determine the parameters that describe the evolution of the degree of reaction, as well as mechanical properties, and allow for the decoupling of values for the total deformation into parts that are related to different physical phenomena. Concluding, this methodology allows accurate prediction of the compressive strength evolution in term of degree of reaction using VEA data carried out within the first 72 hours of the hardening material life. The methodology also leads to straightforward determination of values for the thermal expansion coefficient and the separation of values for autogenous and drying deformation. Furthermore, pilot testing on epoxy mortar demonstrates that the methodology is not limited to cement-based materials Finally, the results of this thesis have the potential to make further contributions to scientific research and to strategies for quality control and safety during construction.

EPFL2005

Modelling shear–flexure interaction in equivalent frame models of slender reinforced concrete walls

Katrin Beyer, Panagiotis Mergos

Quasi-static cyclic tests on reinforced concrete (RC) walls have shown that shear deformations can constitute a significant ratio of the total deformations when the wall is loaded beyond the elastic regime. For slender RC walls that form a stable flexural mechanism the ratio of shear to flexural deformations remains approximately constant over the entire range of imposed displacement ductilities. This paper proposes a method for incorporating shear-flexure interaction effects in equivalent frame models of slender RC walls by coupling the shear force-shear strain relationship to the curvature and axial strain in the member. The suggested methodology is incorporated in a finite element consisting of two interacting spread inelasticity sub-elements representing flexural and shear response, respectively. The element is implemented in the general finite element code IDARC and validated against experimental results of RC cantilever walls. In a second step, it is applied in inelastic static and dynamic analyses of tall wall and wall-frame systems. It is shown that ignoring shear-flexure interaction may lead to erroneous predictions in particular of local ductility and storey drift demands.

2014

Stability of thin reinforced concrete walls under cyclic loads: State-of-the-art and new experimental findings

Katrin Beyer, Angelica Rosso, João Saraiva Esteves Pacheco de Almeida

Damage to structural walls in the recent earthquakes in Chile (2010) and New Zealand (2011) demonstrated that modern reinforced concrete (RC) walls may not achieve the expected ductile response but could possibly be triggered by out-of-plane displacements of the wall. Following a review of the mechanisms that cause global out-of-plane buckling of RC walls, relevant international code requirements, and past experimental tests, this paper describes the findings from quasi-static cyclic tests of two thin RC walls with single layers of vertical and horizontal reinforcement. The two walls were subjected to uni-directional (in-plane) and bi-directional (in-plane and out-of-plane) loading respectively. Both walls experienced significant out-of-plane displacements and damage caused by out-of-plane deformations ultimately triggered the wall in-plane failure. The data obtained with extensive instrumentation of the test units, which included optical measurements of the 3D displacement field, yield new insights into the development of out-of-plane displacements, in particular with regard to: evolution of out-of-plane displacements with imposed in-plane displacements, portion of height and length of the wall that are involved in the out-of-plane instability, influence of both local and global tensile strains on the buckling behaviour and role of bi-directional loading on out-of-plane instability. The tests showed that very significant out-of-plane displacements—larger than half of the wall thickness—can take place without causing out-of-plane wall failure. The damage caused by these large out-of-plane displacements, however, can lead to a premature in-plane failure of the wall.

Springer Verlag2016

Monitoring and modelling of construction materials during hardening

Marco Viviani

EPFL2005