Strategies for rapid seismic hazard mitigation in sustainable infrastructure systems

The goal of this study is to design and evaluate economic and rapid seismic retrofit strategies for relatively small rehabilitation projects for steel structures consistent with the tenets of sustainable design. The need to retrofit existing structures in earthquake prone regions may arise directly from the problem of aging and deteriorating conditions, recognition of the vulnerability of existing infrastructure, from updates in seismic code requirements, or changes in building performance objectives. Traditional approaches to seismic hazard mitigation have focused reducing the failure probabilities, consequences from failures, and time to recovery. Such paradigms had been established with little regard to the impact of their rehabilitation measures on the environment and disruptions to occupants. The rapid rehabilitation strategies proposed here have sustainability benefits in terms of providing a more resilient building stock for our communities as well as minimizing environmental and economical impacts and social consequences during the rehabilitation project. To achieve these goals, a unique approach to design supplemental systems using tension-only elements is proposed. In this design approach undesirable global and local buckling are eliminated. Two rapid rehabilitation strategies are presented. The first is a bracing system consisting of cables and a central energy dissipating device (CORE Damper). The second is a shear wall system with the combined use of thin steel plate and tension-only bracing. Analytical studies using both advanced and simplified models and proof-of-concept testing were carried out for the two devices. The results demonstrated stable, highly efficient performance of the devices under seismic load. Preliminary applications of the CORE damper to the retrofitting of a braced steel frame showed the ability of the system to minimize soft story failures. Both techniques can be implemented within a sustainability framework, as these interventions reduce the seismic vulnerability of infrastructure, are low cost, utilize materials and fabrication processes widely available throughout the world, can be handled by unskilled labor and carried out with minimal disruptions to the environment. The approach taken in this study can provide a road map for future development of sustainability-based rehabilitation strategies.Ph.D.Committee Co-Chair: DesRoches, Reginald; Committee Co-Chair: Leon, Roberto T.; Committee Member: Craig, James I.; Committee Member: Goodno, Barry; Committee Member: White, Donald W

Folded Sandwich Protective Structures against Blast and Impact Loads

In this thesis, novel folded truncated pyramid structures and a bi-directional load-self-cancelling square dome structure are proposed as the core of light-weight protective sandwich structures to resist blast and impact loads. Analytical derivations, numerical simulations, quasi-static and dynamic crushing tests are carried out to examine the dynamic crushing behaviours and energy absorption capacities of various designs for developing the best-performing core structures for blast and impact load resistance

Continuum modeling of paperboard for the mechanical response of converting processes

Paperboard is a thin and lightweight material made of cellulose fibers and it is an important component in packaging material where it provides stiffness and rigidity. The scope of this work is the development of continuum models, and its numerical treatments, for simulating the processes of converting paperboard into packages. The thesis begins with a general introduction to paperboard and a review of modeling approaches are presented. Important continuum modeling concepts used in the papers are presented and key paperboard converting processes are discussed. The main part of the thesis consists of four papers denoted A, B, C and D and they are briefly outlined below.To reduce the computational effort during large scale paperboard forming simulations, a numerical technique which combines a state-of-the-art continuum model for paperboard with state-of-the-art finite element modeling is investigated in Paper A. The model is built up by solid-shell elements where the thickness direction is naturally included in the framework such that the out-of-plane response can be modeled. The approach is validated by numerical studies where the results are compared against fully integrated brick elements. Furthermore, a large-scale forming example for paperboard is explored. Since the loading rate varies during industrial processes and the aim is to maximize the operational velocity, a rate-dependent continuum model for paperboard is developed in Paper B. The new rate-dependent model is based on the static material model in Paper A which is enhanced with a viscoelastic and viscoplastic framework. The developed model is calibrated using uniaxial experiments and evaluated against line-creasing and line-folding measurements. In Paper C, the continuum model in Paper A is enhanced to include continuum damage. Damage is needed to adequately capture the mechanical response during sequential loading of creasing and folding. A scalar isotropic damage variable is introduced and the damage evolution is calibrated for a reference mesh during folding. A simple scaling strategy is introduced to reduce the mesh dependence due to damage evolution. To showcase the proposed model, an illustrative $3$D example is presented where a paperboard sheet is creased and folded to mimic the corner folding process. In Paper D, an experimental device and a protocol is developed for cyclic uniaxial out-of-plane compression and tension measurements. This load case is important since it is present during creasing and subsequent folding where the material is subject to large out-of-plane compressive stresses followed by out-of-plane tension and delamination. The soft initial load-displacement response during compression is shown to stem from the surface roughness and not a material property. In addition, the experiments show that the transition from compression to tension is smooth. Consequently, a switch function, previously introduced in literature that separates the elastic behavior between compression and tension, is deemed as questionable for continuum modeling

Active control of passive safety in passenger motor vehicles : a feasibility study investigating dynamic denting of members using pyrotechnic devices

This report describes a feasibility study investigating dynamic denting of members using pyrotechnic devices to engineer favourable energy absorption characteristics into thin walled tubes. A tube of sufficiently low slenderness ratio and wall thickness, when loaded axially to failure, will collapse in the progressive buckling mode. After the ultimate buckling load has been exceeded, and as the tube continues to compress, the load oscillates between loads considerably lower than the ultimate buckling load. The object of introducing an advantageous deformation is to decrease the ultimate buckling load to a magnitude comparable with the subsequent peak loads, but at the same time avoiding a change in the buckling mode which is not advantageous. Testing was limited to thin walled square mild steel tubes. The test procedure began with a process to determine the limitations imposed on the geometric imperfections that could be achieved by the use of explosive. It was found that all the explosively induced deformations were rounded, i.e. the dents were hemi-spherical in shape. It was also found that a smooth edged round hole could be created in the centre of the dent with the use of a round, flat explosive charge. Geometric imperfections that could be induced explosively in the specimens (as well as other deformation shapes, tested for comparative purposes) were mechanically formed in the specimens. The tubes were then quasi - statically crushed to determine the energy absorption characteristics induced by the deformations. When spherical dents were induced, the deformation affected the tube beyond the immediate spherical dent and hence the distance between the plastic hinges was increased and instabilities in the crushing process were introduced. Holes (without any visible denting) decreased the distance between the plastic hinges and thus also induced instabilities. In both cases the tubes tended to skew over to one side and in extreme cases Euler buckling ensued

Energy absorption of car chassis rails under impact conditions

Although the levels of safety offered to the occupants of cars has improved considerably in the recent past, car users still comprise more than 50% of all European road user fatalities. The predominant accident type experienced is a frontal impact with another car. at speeds below 64 kmh (40 mph). This type of accident is reproduced by the new European offset deformable barrier frontal impact test requirement which supplements the fully distributed. rigid barrier impact test that is still required in many countries around the world

The mechanics of composite corrugated structures: A review with applications in morphing aircraft

Corrugation has long been seen as a simple and effective means of forming lightweight structures with high anisotropic behaviour, stability under buckling load and energy absorption capability. This has been exploited in diverse industrial applications and academic research. In recent years, there have been numerous innovative developments to corrugated structures, involving more elaborate and ingenious corrugation geometries and combination of corrugations with advanced materials. This development has been largely led by the research interest in morphing structures, which seek to exploit the extreme anisotropy of a corrugated panel, using the flexible degrees of freedom to allow a structure’s shape to change, whilst bearing load in other degrees of freedom. This paper presents a comprehensive review of the literature on corrugated structures, with applications ranging from traditional engineering structures such as corrugated steel beams through to morphing aircraft wing structures. As such it provides an important reference for researchers to have a broad but succinct perception of the mechanical behaviour of these structures. Such a perception is highly required in the multidisciplinary design of corrugated structures for the application in morphing aircraft