Long-term design of FRP-PUR web-core sandwich structures in building construction

The structural behavior of GFRP-polyurethane (PUR) web-core sandwich structures subjected to sustained loading was investigated. As a basis, a study of the mechanical behavior of rigid PUR foams used as core materials was conducted, with emphasis on creep. The study showed that the foam anisotropy, its density and the loading type applied must be considered to assess the structural performance of the GFRP-PUR web-core sandwich. The influence of creep on the web-core interaction, i.e. on the shear load distribution and local instability phenomena were then analyzed. The effects of applying particular design recommendations on the design were assessed based on the example of a real GFRP-PUR sandwich roof. The design shear resistance of the GFRP webs, their dimensions and governing failure mode significantly depended on the applied recommendation. A design procedure to evaluate the overall shear resistance of the GFRP-PUR core over time, taking into account creep effects, was presented. (C) 2017 Elsevier Ltd. All rights reserved.

Seismic Behaviour and Design of Mixed RC-URM Wall Structures

Alessandro Paparo

In several countries of central Europe, many modern residential buildings are braced by reinforced concrete (RC) and unreinforced masonry (URM) walls coupled with RC slabs. Such mixed constructions, in fact, behave better under seismic loading than buildings with URM walls alone. Similarly, the insertion of RC walls is a technique used to retrofit existing modern URM constructions that feature RC slabs, since both strength and displacement capacities of the repaired structure increase with respect to the un-retrofitted configuration. Although modern mixed RC-URM wall buildings are rather common, very little is known about their seismic behaviour and codes do not provide adequate design and assessment guidelines. Hence, the thesis focuses on four objectives: (1) to provide experimental data on the seismic behaviour of mixed RC-URM wall structures; (2) to formulate recommendations for setting up numerical models for structures with both RC and URM walls; (3) to develop a mechanical model that represents the interaction between RC and URM walls; (4) to propose a displacement-based seismic approach for the design of new mixed RC-URM wall structures and the retrofitting of URM wall buildings by adding RC walls or replacing URM walls with RC ones. An experimental investigation of two mixed RC-URM wall substructures leads to new findings with respect to the actual distribution of the reaction forces between RC and URM walls and gives insight into the displacement profile of mixed RC-URM wall structures. The results are used to validate two numerical strategies and recommendations for setting up models for structures with both RC and URM walls are formulated. A simple mechanical model, which takes into account the most important parameters influencing the seismic behaviour of mixed RC-URM wall structures, is proposed and validated. The model is based on the shear-flexure interaction as URM and RC walls display dominant shear and flexural deformations, respectively. In the last part of the thesis a displacement-based design approach for mixed RC-URM wall structures is developed. The design method is verified through inelastic time-history analyses (ITHA) of three-to-five-storey case study buildings. Comparison between the design values and the results from ITHA suggests that the design methodology controls the horizontal deflection of the structures, being almost linear over their height, and avoids concentrations of deformations in the bottom storey, a typical feature of URM wall structures. On the other hand, for the three-storey configurations, it was observed that the approach overestimates the maximum horizontal displacement.

EPFL2015

Design and Control of Minimum Energy Adaptive Structures

Gennaro Senatore

The construction industry is the largest consumer of raw materials and most of the environmental impacts of structures are embodied into load-bearing systems [1]. Civil structures are usually designed to meet strength and deformation requirements to withstand rare events such as earthquakes and strong winds which in practice occur very rarely. Most structures are thus overdesigned during their service life. Instead, structures could be adaptive to counteract the effects of external loads through sensing and actuation. A new optimum design methodology for adaptive structures has been formulated by Senatore et al. [2]. The main objective is the minimization of the whole-life energy which encapsulates material and operational energy minimization. Instead of relying only on passive resistance through material mass, an actuation system is optimally integrated to alter the flow of internal forces and to change the shape of the structure. The internal forces are controlled to achieve stress homogenization and the shape is changed to control deflections or to morph the structure into optimal shapes as the load changes [3]. To ensure the embodied energy saved this way is not used up to by actuation, the adaptive solution is designed to cope with ordinary loading events using only passive load bearing capacity whilst relying on active control to counteract larger events with a smaller probability of occurrence. Extensive numerical simulations show that the whole-life total energy could be reduced by up to 70% when the design is stiffness governed (e.g. slender structures, strict deflection limits) [4]. A large scale prototype was successfully tested demonstrating the feasibility [5]. Structural adaptation allows a much more efficient utilization of material resources, thus lowering environmental impact. Adaptive structures can be extremely slender while still being capable of reducing deflections at the expense of a small amount of operational energy. This allows for taller and more slender buildings resulting in increased floor area via reduction of structural cores as well as longer span bridges and self-supporting roof systems. Combining these aspects is unique in structural engineering. References

2019

Seismic Behaviour and Design of Mixed RC-URM Wall Structures

Alessandro Paparo

EPFL2015

Design and Control of Minimum Energy Adaptive Structures

Gennaro Senatore

2019