The newly upgraded UC San Diego shake table allows researchers across the US to replicate the combined effect of all the motions of an earthquake applied to a structure, as well as the interaction between soil and building, and soil liquefaction. Testing infrastructure at large scale, under realistic multi-degree of freedom seismic excitation, is essential to understand fully the seismic response behavior of civil infrastructure systems.
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KEY RESEARCH FOCUS AREAS
Unreinforced masonry buildings
The LHPOST6 will enable the robust assessment of the seismic safety of URM buildings and the development of effective retrofit and strengthening methods.
Steel buildings
The LHPOST6 can facilitate research to assess interactions in building systems undergoing earthquakes. Shake table testing will aid in assessing problems such as competing inelasticity in vertical and horizontal lateral- force resisting systems, overstrength and system effects derived from the participation of gravity, and non- structural framing in lateral response.
Structural concrete systems
Experiments on the LHPOST6 can help develop innovative, resilient, seismic-resistant concrete systems under multi-axial excitation, specifically to improve modeling and analysis capabilities for component and system behavior. Engineers are particularly interested in using high strength materials (reinforcing bars and concrete) and advanced materials for seismically resilient civil applications. This entails testing special concrete moment frames and structural walls, including the combination of dual systems; precast concrete frame, and wall structures; and sustainable reinforced concrete structures utilizing recycled materials.
Uniaxial test validation
Current design standards rely on 3D computational models of structures to extrapolate results of uniaxial shake table tests to project structural performance under multi-axial loading conditions. The lack of pertinent data to validate the accuracy of computational models for these predictive analyses is an important issue. Multi-axis shake table tests are needed to study more realistically the behavior of civil structures and to improve current seismic design methods and standards.
Non-structural components and systems
The scarcity of full-scale building shake table tests that incorporate NCSs limits our understanding of the seismic response of these non-structural components.
Limited recent tests, supported by field observations, demonstrate the importance of advancing our understanding and predictive capabilities under multi-directional loading of NCSs in building systems. Full-scale multi- axial shake table tests are needed to advance the development of a reliable, unified design strategy for NCSs accounting for multi-directional earthquake excitation.
Protective systems
Extensive damage in conventional buildings has caused a push in earthquake-affected communities in the past two decades to use low-damage structural earthquake protective systems. Such systems can sustain significant nonlinear response, large lateral displacements, and damping with practically no damage and maintained operability after strong earthquake ground motions.
This is an active research area that includes base isolation, rocking foundations and systems, self-centering systems, inertial force-limiting floor anchorage systems, dampers, buckling-restrained braces, and new materials. This is an active research area that includes base isolation, rocking foundations and systems, self-centering systems, inertial force-limiting floor anchorage systems, dampers, buckling-restrained braces, and new materials.
Soil structure interactions
The LHPOST6 is ideally suited for experimental investigations of dynamic SSI. Three general types of experimental SSI studies are:
- Verification studies under tri-axial excitation: With verification studies under tri-axial excitation, computer models of the complete soil, foundation, structure system can be used to obtain the total translational and rotational motion of the foundation, which can then be applied at the base of the structure placed on the LHPOST6. The resulting experimental motion of the structure can be compared with the numerical simulation to validate both the theoretical model and computational method.
- Hybrid tests: Hybrid tests could be used to study the non-linear seismic response of structures in the presence of soil-structure interaction, as well as studies of the torsional response of structures. And large soil box tests under tri-axial excitation could be used to study the nonlinear response of soils, the response of partially saturated soils, and the non-linear interaction of foundations, structures, and the soil.
- Geostructures: Soil foundation-structure interaction (SFSI) tests can be used to study the performance of underground structures (such as energy vaults, pipelines, and deep and shallow tunnels), bridge abutments, earth retaining walls, levees, embankments, large cut and fills, and slope stability in hillside construction. The LHPOST6 can support the testing of underground pipelines subject to liquefaction loads or fault crossing demands by taking advantage of the large displacement capacity of the LHPOST6, enabling researchers to conduct large-scale dynamic testing of underground facilities and pipelines and techniques for evaluating ground movement patterns and stability for a variety of excavation, tunneling, micro-tunneling, and mining conditions.
Energy/Power structures
There is a strong emphasis on the need to develop new sources of energy while preventing or reversing the degradation of the environment (i.e., renewable energy sources). Important examples of the supporting infrastructure include wind turbine farms (onshore and offshore), solar arrays, concrete dams, containment/reactor vessels of nuclear power plants and dry storage casks of spent nuclear fuel, which when built in seismic regions, all require better understanding of their seismic response behavior and reliable performance-based assessment and design using experimentally validated high-fidelity computational models.
Bridge structures
The 1971 San Fernando and 1989 Loma Prieta Earthquakes were a turning point in the seismic design
practice of bridges not only for California but for all seismic-prone regions in the United States. The Caltrans seismic retrofit program made large gains in designing retrofit strategies for existing bridge components with known vulnerabilities as well as developing new design strategies.
A great challenge in the seismic design of slender columns that are part of a complex highway interchange system is to properly evaluate its response under the combined effects of vertical and bi-directional horizontal excitations. The capabilities of the LHPOST6 will open a new paradigm shift in properly evaluating the seismic response of slender columns and many other complex structures and validating the high-fidelity modeling of nonlinearly responding bridges, including soil-structure-
interaction and liquefaction effects in the case of soils vulnerable to liquefaction.
Structural health monitoring
Condition assessment of structures plays a key role in supporting the decision-making process following natural or artificial hazard or aging events. These events, such as earthquakes, can potentially induce critical damage to civil structures, and subsequent decision-making related to emergency response, inspection, evacuation, and retrofit of structures is of vital importance.
Damage initiation and progression cannot always be detected through visual screening and, therefore, time-consuming, costly, and invasive post-event inspection and evaluation methods are required to detect certain types of damage. Potential impacts of earthquakes as well as other natural and man-made hazards on communities can be reduced through accurate and timely risk mitigation decisions after catastrophic events, which can be supported and facilitated by the use of structural health monitoring (SHM), diagnosis, and prognosis methods to help assess the damage in, and residual strength of, civil structures.
Liquid storage tanks
Liquid storage tanks (LSTs) are critical structural system elements in the industry. These tanks are used in chemical processes, water, fuel, oil and gas storage and for fermentation of alcoholic beverages, among many uses. Poor seismic performance of LSTs was observed in recent earthquakes in Chile, New Zealand, Italy, and the 2014 South Napa earthquakes.
The LHPOTS6 is a unique facility where much needed research can be conducted to evaluate, develop high-fidelity models that include the fluid-structure and soil-fluid-structure interaction, and improve the seismic response of storage tanks, with smaller tanks tested at full-scale and large tanks tested at reduced scales, for example in the range of 1:10 to 1:20.
Additive manufacturing (3D printing)
Rapid prototyping of 3-dimensional parts (also termed 3D printing) with cementitious or metallic materials allows geometrically intricate but efficient designs which are today unfeasible to construct using traditional methods.
Researchers in 3D printed construction can benefit from testing on the LHPOST6 to investigate the performance of these structures under dynamic excitation. The goal would be to support the development of large-scale additive manufacturing technologies capable of efficiently producing multifunctional structural elements with enhanced performance. This development includes the need for standardized testing and quality control, investigating ways to print using multiple materials, and combining additive manufacturing with other processes as hybrid techniques.
CRITICAL NEED FOR LARGE OR FULL SCALE SYSTEM LEVEL TESING
- The seismic response of structures involves complex physics of heterogeneous materials with highly nonlinear constitutive properties and depends on the boundary/interface conditions, such as the interaction between the structure and the supporting/surrounding soil.
- There are many open and profound issues and questions regarding how to accurately model these phenomena at the different length and time scales over which the physical processes develop.
- State-of-the-art nonlinear structural analysis methods are still fairly limited in their ability to model the nonlinear dynamic response of structures, especially when approaching collapse (e.g., local buckling and fracture in steel, shear failures, connection or splice failures).
- The boundary conditions imposed on tests of individual structural components or sub-assemblies may not be realistic as compared to their actual boundary conditions within the structural systems.
- Scale of physical models is an issue since some design details, construction materials, and damage and failure mechanisms cannot be accurately reproduced in reduced-scale models (e.g., spacing of reinforcement, size of aggregates, quality and properties of welds, and degree of plastic strain or damage localization).
LHPOST6 NETWORKING GROUP
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