Development of Inelastic Panel Zone Database

This data paper reviews the experimental research on fully restrained beam-to-column connections for steel moment-resisting frames (MRFs) over the last 50 years worldwide and presents an experimental database consisting of 100 tests with an emphasis on those exhibiting inelastic panel zone behavior. The collected data, which is organized in a consistent format, includes full digitized histories of the local panel zone shear force-shear distortion as well as the global force-displacement hysteretic diagrams of each experiment. In most cases the original data was only available in paper format. The gathered dataset suggests that the existing panel zone models that are currently used for the seismic design of steel MRFs deviate, in some cases considerably, from the measured response quantities of an actual panel zone. These involve the panel zone stiffness and shear resistance at selected inelastic shear distortions of interest to the engineering profession. The assembled inelastic panel zone database provides ranges in which post-Northridge beam-to-column connections, which exhibit considerable inelastic deformations within the panel zone web, may achieve lateral drift demands larger than 4% without experiencing premature fracture. The assembled dataset constitutes an important source for validation of continuum finite-element models that could aid the simulation-based engineering design of steel MRF beam-to-column connections designed with a balanced design approach. The database is made available to the engineering and research communities through a publicly available data repository. (C) 2021 American Society of Civil Engineers.

A Structural Design Methodology for Freeform Timber Plate Structures Using Wood-Wood Connections

Anh Chi Nguyen

Over the past decades, timber has gained popularity as a sustainable building material because of the rising environmental awareness. Furthermore, the resurgence of timber has also been encouraged by the advent of the digital age during the 21st century. The development of computer-aided design programming and digital fabrication tools has stimulated significant advances in both architecture and engineering. Within this context, researchers have shown a growing interest in wood-wood connections, inspired by traditional woodworking joints. Geometrically complex timber structures assembled with joints integrated in their plates have been developed using algorithmic geometry processing. However, although their design and fabrication have been automated, research focused on automated numerical tools for their structural analysis has been very limited. This thesis is providing a design methodology for the structural analysis of timber plate structures composed of a large number of discrete planar elements and wood-wood connections. A finite element model, in which the semi-rigid behaviour of the connections is implemented using springs, is proposed. It is applied to a specific case study, namely the Annen Plus SA head office project in Manternach, Luxembourg, which consists of a series of double-layered double-curved timber plate shells. A design framework is introduced to automate the generation of the model and integrate structural analysis into the existing design and fabrication workflow. The numerical model was built for both small- and large-scale structures through custom scripts and subsequently assessed through experimental investigations: first, laboratory tests were performed on small assemblies with simplified geometry; secondly, a displacement study was carried out onsite on a 24 m span structure. Results obtained with the semi-rigid spring model were found to be in good agreement with experimental tests. The proposed model was therefore validated for the serviceability limit state. Furthermore, the semi-rigidity of the connections in translation as well as in rotation was shown to highly influence the model and is therefore crucial for the accuracy of the model. Based on experimental tests observations, an alternative structural system was proposed and compared to the initial one through numerical investigations within the proposed design framework. A significant influence on the structureâs performance was found, demonstrating the possibilities for structural optimisation. Finally, a three-dimensional finite element model for wood-wood connections was investigated. It aimed to predict their semi-rigid behaviour, generally characterised through experimental tests, necessary for their implementation in global models. The material model was evaluated based on shear load tests performed on different engineered wood products. Stiffness and load-carrying capacity of the connections were approximated with numerical simulations. However, experimental tests remain necessary to precisely predict the behaviour of the joints. This thesis highlights the importance of adopting an integrated design strategy encompassing engineering and fabrication aspects for geometrically complex timber structures, as well as establishing a link between local behaviour of the connections and global behaviour of the structure. The gained knowledge can facilitate the design and realisation of large-scale freeform timber structures with wood-wood connections.

EPFL2020

Adhesively bonded lap joints of pultruded GFRP shapes

Till Vallée

The importance of Fibre Reinforced Polymers (FRPs) as a material used for civil engineering purposes has grown in the last decade. Especially the introduction of pultrusion at an industrial level as a way to produce big batches of FRP made it possible to offer the advantages – like the high strength-to-weight ratio or the good corrosion resistance – at a reasonable cost. One issue when designing with pultruded FRPs are the connections. Up to now, connections between pultruded FRPs have been designed in the same way as structural steel connections, mainly through bolts. Because of the fibrous and layered character and the anisotropy of pultruded FRPs, bolting is not a material-adapted way to connect. Adhesive bonding is by far better suited, but has not yet been investigated for the special case of pultruded FRPs. This research is intended to fill the gap by offering designing engineers a method allowing them to dimension safe and economic adhesively bonded joints of pultruded FRPs under static loads. The present Thesis is aimed to show the steps leading to this method. After a short introduction, where the objectives and methods used are listed, the actual state of the art is presented. The review of actual literature shows that not much has been done on the special field of adhesively bonded connections of pultruded FRPs, neither experimentally nor theoretically. Some publications treat the global aspect of bonded connections for special cases like the single and double lap joints, but all on idealized mechanical systems with isotropic adherents. Also, there are no detailed reports of a mechanical failure criterion for both describing and quantifying the failure of pultruded FRPs. To overcome this, experimental investigations were carried out at different levels: the basic FRP material has been investigated in both senses of revealing the fibre architecture – with the help of burn-off tests – and the material strength – using a device the Author especially developed for this purpose: the CCLab Shear-Tensile device. This device allows the determination of the material strength subjected to combinations of out-of-plane and shear stresses. The device was also used to determine an important basic material property necessary to numerically formulate the anisotropy: the out-of-plane E-Modulus. Besides the investigations on the basic material, experiments on bonded single and double lap joints were carried out where the influence of parameters like the length of the bonded overlap, the thickness of the adherents and stress reduction methods (like chamfers of fillets) on the ultimate load was investigated. All of these experimental investigations were carried out on relatively big specimens to avoid the influence of any size effects. The experimental results showed that the adhesive layer thickness and stress reduction measures like chamfers are by far less influential that former publications expected them. For selected geometric configurations, the axial strain development along the bonded splice was experimentally gathered using strain gauges. Comparisons with FEA showed that by using the right mechanical input parameters in regard to the anisotropy, it is possible to model, with sufficient accuracy the stresses inside adhesively bonded joints of pultruded FRPs. Some single and double lap joints were filmed using a high-speed camera (up to 2000 fps) to investigate the failure process. This failure process is closely linked to the fibre architecture in the sense that it has been shown that the failure is triggered inside the laminate. The entire group of experimentally investigated specimens were then modeled with the Finite Element Method using orthotropic elements. In combination with the experimentally gathered material failure criterion, it was possible to formulate a method based on the comparison of stresses in the joint and the material resistance to predict the ultimate load of single and double lap joints, which was validated for a wide range of geometrical configurations. A simplified version of this method, based on existing analytical formulae, was then developed to make the strength prediction of adhesively bonded joints of pultruded FRP shapes available for civil engineering purposes.

EPFL2004

Acceleration and inclination sensors based on magnetic levitation

François Barrot

Some fields such as the Monitoring of Civil Engineering Structures, need very sensitive acceleration and inclination sensors with a high resolution at low accelerations (typically less than 1G) and moderate frequencies (typically less than 20 Hz) or very small inclinations (typically less than 1°). The instruments currently available for such measurements are either very high precision instruments (hence very costly), used in seismology and globe physics or cheaper products lacking the sensitivity needed and having inadequate measurements ranges both in frequency and intensity. Such a situation hinders considerably the updating of construction codes in seismic zones as well as the study of the complex soil-structure interaction phenomenon in risk areas. This thesis proposes to study the utilization of magnetic levitation for designing acceleration and inclination sensors, simple and sensitive enough to meet the needs of particular applications like the monitoring of civil engineering works. Levitating the seismic mass of an inertial sensor does free its design of all the constraints created by a mechanical link between the inertial mass and the base of the instrument, which render present instruments so complex and so expensive. Two levitation techniques have been investigated and used for designing and testing two prototypes. A triaxial acceleration sensor using the Active Magnetic Bearings technique and an uniaxial inclination sensor using passive diamagnetic levitation have thus been implemented and tested. Experimental results obtained with these prototypes are not better than those obtained with instruments currently available, but they do validate the concept. As part of this research, active magnetic levitation has been investigated under an angle somewhat different from its classical application since its use for the design of sensors is subject to constraints rather different from those inherent to its use as a bearing. Furthermore, since up to now, diamagnetism has found very few applications in engineering, the present study proposes an analytical model along with design criteria that can be used as a starting point for the study and implementation of micro-mechatronic systems based on diamagnetic levitation.

EPFL2008