Seismic loading | EPFL Graph Search

Seismic loading is one of the basic concepts of earthquake engineering which means application of an earthquake-generated agitation to a structure. It happens at contact surfaces of a structure either with the ground, or with adjacent structures, or with gravity waves from tsunami. Seismic loading depends, primarily, on:

Anticipated earthquake's parameters at the site - known as seismic hazard
Geotechnical parameters of the site
Structure's parameters
Characteristics of the anticipated gravity waves from tsunami (if applicable).

Sometimes, seismic load exceeds ability of a structure to resist it without being broken, partially or completely Due to their mutual interaction, seismic loading and seismic performance of a structure are intimately related. See also *Earthquake engineering structures

Seismic Retrofitting of Existing Steel Structures With Buckling Restrained Bracings

Ariele Forni

The objective of this project is the seismic retrofit of an existent steel structure with buckling restrained braces (BRBs), and the proposition of a possible heightening. The structure that will be analysed is the GC building on the EPFL campus, in Ecublens. The structure has already been analysed in some previous studies and it has been highlighted that its seismic behaviour does not comply with current standards. Some solutions have already been proposed, as the reinforcement of gusset plates and the use of friction dampers. In this project a new solution will be evaluated, using BRBs to retrofit the structure. The advantage of this technology is that the structure becomes more flexible and at the same time more stable under a seismic load. In fact, BRBs do not experience buckling and their behaviour is hysteretic. With this new design, the number of connections and braces can be halved, decreasing the cost of the structure and eliminating weak points. A heightening of the structure will also be studied, as it was originally designed to be taller, and the EPFL is searching solutions for increasing the campus capacity.

2021

Experimental Behavior and Nonlinear Modeling of iron-based Shape Memory Alloys (SMAs) under Inelastic Cyclic Straining

Diego Isidoro Heredia Rosa

Shape memory alloys (SMAs) have gained considerable attention in a broad range of engineering applications. In particular, iron-based SMAs (Fe-SMAs) have been recently developed and used as a cost-eﬀective method for prestressed-strengthening of civil structures. Previous studies have shown that Fe-SMAs oﬀer a strong shape memory eﬀect (SME), however, a negligible superelastic behavior. The potential use of Fe-SMAs in seismic design and retroﬁt applications including supplemental damping is not yet clear and requires the further understanding of the material behavior under large amplitude cyclic inelastic straining. This thesis discusses key ﬁndings from a material-level experimental program that involved Fe-SMA round coupons subjected to a broad range of uniaxial cyclic strain histories representative of earthquake loading. Also, this work discusses the nonlinear modeling of Fe-SMAs under cyclic tension/compression straining.

2020

Experimental investigation of the cyclic properties of welds in mild structural steels

Selimcan Ozden

Structural steels have long been used in construction applications. Their mechanical properties and behavior under seismic loading or under fatigue design are of considerable interest for researchers and engineers. Although extensive studies have been conducted on the cyclic behavior of structural steels, they mostly focus on base material responses. However, base material response can be affected by changes in microstructural properties of steels. In steel construction this situation often arises in welding different components where due to thermal loading certain regions change their crystallographic phases and consequently their mechanical properties. This master's thesis is dedicated to the investigation of the lesser known large amplitude cyclic material behavior of these regions termed Heat Affected Zones (HAZ). The behavior of welded connections is of paramount importance for structural integrity. Their behavior under extreme loading conditions can be the determining factors for the failure of joints and subsequent structural collapse. Field observations following significant earthquake events (e.g. 1994 Northrigde incident) has shown that the assumed ductility of the steel construction can be put into question when poorly executed welded structural joints suffer premature fracture. The head-boomed experience from these suggests that failures often arise from combination of ill-conceived detailing and insufficient weld quality (e.g. large defects on low thoughness). As the understanding of this problem progressed, better detailing properties and quality controls have been proposed to avoid brittle nature of joint failure. In this master’s thesis the author investigates the behavior of S355J2+N structural steel as HAZ of welded material and base material subjected to uniaxial cyclic loading and large inelastic strain demands under seismic loading in the experimental and numerical level. HAZ at welded specimens is obtained through thermal loading in the laboratory environment. Uniaxial cyclic loading tests are performed in the laboratory as well. In addition, comparisons between the base and welded metals for the steel class of S355J2+N are provided as well including material parameters for Voce-Chaboche and Updated Voce-Chaboche models. Results of this study reveal that under cyclic loading welded material hardens more than base material. In addition, plateau region exercised in base material disappears in welded material and welded specimens experience rounding around the yield stress which is not the case for base material. Accuracy of simulation of welded material and correctness of model parameters greatly depend on whether Voce-Chaboche or Updated Voce-Chaboche model is applied to the right material being investigated.

2021

Experimental investigation of the cyclic properties of welds in mild structural steels

Selimcan Ozden

2021