Energy-based Design Procedure Research Articles

Energy-Based Design of Buckling-Restrained Steel Braced Frames for Concurrent Occurrences of Earthquake and Wind

This paper describes the development of a dual hazard spectrum for use in the dynamic analysis of steel frames subject to the combined effects of earthquakes and wind. The proposed spectrum is obtained by combining the power spectra of earthquakes and wind using the square root of the sum of squares (SRSS) combination method. An equivalent time excitation function is then computed using an inverse fast Fourier transform (IFFT) and serves as input for the dynamic analysis. Using time-history analysis on the OpenSees platform, the dynamic responses expressed in terms of peak and residual inter-story and roof drifts for two multistory steel frames located in two US cities (Los Angeles and Charleston) are obtained to demonstrate that designing these buildings based on just one hazard may not be adequate. For frames that are considered under-designed, an energy-based design procedure that uses buckling-restrained braces (BRBs) to dissipate the excess energy imparted to these frames is proposed so they will satisfy the FEMA 356 recommended drift limits for the performance levels of immediate occupancy and life safety.

Application of an energy-based design procedure in self-centering shear wall systems

Application of an energy-based design procedure in self-centering shear wall systems

Novel design procedure for steel hysteretic dampers in seismic retrofit of frame structures

An energy-based design procedure for sizing dissipative bracing systems equipped with steel hysteretic dampers is proposed for application to the seismic retrofit of frame structures. The procedure is based on the following assumptions: it is not iterative, as it provides a direct estimation of the steel dissipater sizes; the stiffening effects of dampers reduce displacements below prefixed limits; their damping effects reduce displacements and stress states to keep the response of structural members within their safe domains up to medium-to-high levels of the input seismic action. The procedure is articulated in three steps: seismic assessment analysis in current state and definition of the elastic properties of the bracing system to be installed in the structure; design of the dampers; verification of the seismic performance of the structure in retrofitted conditions. A demonstrative case study concerning a precast reinforced concrete frame school building is offered to explicate the practical application of the procedure, as well as to evaluate the enhancement of its response generated by the intervention. The latter consists in incorporating a dissipative bracing system equipped with triangular-shaped added damping and stiffness (T-ADAS) steel hysteretic devices. The two limit hypotheses assumed in the computational analyses for the roof beam-to-column connections of the building, i.e. hinges or fixed-ends, allow to discuss how the fundamental period of the structure in current conditions affects the parameters involved in the sizing process of the T-ADAS dampers.

An improved equivalent energy-based design procedure for seismic isolation system of simply supported bridge in China's high-speed railway

The high-speed railway (HSR) in China has developed rapidly in recent years. However, HSR bridges have to face the challenge of earthquakes since China is one of the most earthquake-prone countries in the world. Bearing is the key component in the HSR bridge, and using isolation bearing instead of common bearing (non isolation bearing) can provide bridge the better seismic performance. To improve seismic performance of HSR bridges at different earthquake intensities, in this paper the friction pendulum bearing (FPB) is used, and an improved equivalent energy-based design procedure (EEDP) based on the principle of energy conservation is proposed. This method has the advantages of simple calculation and avoiding complicated iterations, which can also take into account the post-yield stiffness of the structural members and is capable of designing three performance objectives simultaneously. Meanwhile, based on the analysis of experimental data, the improved performance objectives applicable to the isolated HSR bridges are proposed. The FPB of an isolated HSR bridge is designed by the improved EEDP to verify the applicability of the proposed method. Then the finite element model of the designed isolated HSR bridge is built, and nonlinear dynamic responses at different earthquake intensities are analyzed to examine the structural seismic performance. Results show that the designed structure can achieve the prescribed performance objectives at three earthquake intensities which proves the practicability and effectiveness of the proposed improved EEDP method.

Verification of an energy-based design procedure for seismic retrofit of a school building

A viable design criterion of supplemental damping strategies for seismic retrofit of frame structures, recently proposed by the first author (Terenzi, 2018), is applied in this paper to a school building in Florence dating back to the early 1980s. The building is composed of two portions, with reinforced concrete and steel frame structure, respectively. Similarly to several other buildings of the same period, the structure is infilled by heavy reinforced concrete panels interacting with the frame elements under horizontal loads. A careful reconstruction of the structural characteristics of the constituting members, based on the original design documentation and on-site testing campaigns, highlighted specific drawbacks in current state, related to a remarkable degration of the materials and a poor performance of several elements. The retrofit solution considered in this study consists in removing the infill panels and replacing them with a set of dissipative braces incorporating fluid viscous dampers as protective devices. The design is carried out by the sizing criterion mentioned above, targeting an elastic structural response up to the maximum considered earthquake normative level.

Earthquake retrofitting of R/C frames with soft first story using hysteretic dampers: Energy-based design method and evaluation

Soft stories constitute a major reason for building collapses during severe earthquakes. This paper investigates a solution for the seismic upgrade of existing reinforced concrete frames with open first story and masonry infills at the upper stories. It combines the addition of hysteretic dampers with the strengthening (if necessary) of the columns of the first story. The energy-based design procedure put forth provides the strength, stiffness and energy dissipation capacity required for the dampers so that the overall structure can endure the design earthquake without exceeding a prescribed maximum drift at the first story. The strength required for the dampers depends on the strength of the columns of the first story therefore multiple solutions are possible. The proposed method takes into account the contribution of the elastic deformation of the upper stories to the elastic vibrational energy, using simple formulae to determine the strength for these stories that will guarantee they remain elastic. Finally, non-linear dynamic analyses are carried out to evaluate the seismic performance of the retrofitted structures and to validate the proposed procedure.

Numerical Models and Seismic Design of Steel Frames Equipped with Supplemental Fluid Viscous Devices

Numerical investigations were conducted to assess the seismic performance of steel frames equipped with supplemental viscous damper devices. The study was based on experimental results of pseudo-dynamic tests carried out on a prototype steel frame at the JRC Ispra. A finite element assembly reproducing the observed behaviour of fluid viscous devices was developed and implemented in numerical models of multi-story steel frames. An energy based design procedure was applied to determine the damping properties of the devices and the seismic response of two multi-story steel frames was investigated. Comparison of the seismic response of the frames with and without viscous dampers indicated that the application of this innovative technique is very effective in attenuating the effects of seismic actions on structures. The effectiveness of the damper braces was also evaluated through a comparison with a traditional undamped bracing solution. The frames protected with fluid viscous devices exhibited smaller interstory drifts compared to the unprotected frames and smaller story shear forces compared to frames with traditional bracing system due to the energy dissipation provided by the fluid viscous devices.