Modified Partial Capacity Design (M-PCD): achieving partial sidesway mechanism by using two steps design approach

Partial Capacity Design (PCD) has been developed by using magnification factor to keep some columns undamaged during major earthquake. By doing so, the structures will experience the partial side sway mechanism which is also stable, instead of the beam sidesway mechanism. However, in some cases, structures designed by PCD method failed to show the partial side sway mechanism since unexpected damages were still occurred at some columns. In this research, modification of PCD method is proposed by using two structural models in the design process. The first model is used to design beams and columns which are allowed to experience plastic damages, while the second model is used to design columns which are intended to remain elastic when the structure is subjected to a target earthquake. Two nominal earthquakes corresponding to Elastic Design Response Spectrum (EDRS) level with seismic modification factors (R) of 8.0 and 1.6 are used in the first and second structural models, respectively. It should be noted that the second model is identical to the first model except that the stiffnesses are reduced for elements to simulate potential plastic damages. This proposed method is applied to symmetrical 6 and 10 storey buildings with seismic load according SNI 1726:2012 and with soil classification of SE in Surabaya city. A Non-linear Static Procedure (NSP) or pushover analysis and Non-linear Dynamic Procedure (NDP) or time history analysis are employed to evaluate the performance of the structure. The evaluation is conducted at three earthquake levels which are nominal earthquake that is used in second model, earthquake corresponding to EDRS level, and maximum considered earthquake (MCER) specified by the code (50% higher than EDRS level). The building performances satisfy the drift criteria in accordance with FEMA 273. However, the partial side sway mechanism was not achieved at NDP analysis at maximum seismic load, MCER.

Study on Response Spectrum of Seismic Design of Ultra High Voltage Converter Valves in Bedrock Site

It is difficult to evaluate seismic performance of ultra-high voltage (UHV) converter valves reasonably because the response spectrum period used in seismic design of electrical equipment fails to cover the structural period of UHV converter valves at present. Bedrock response spectrum is the basis of seismic design response spectrum. 471 records of long period strong earthquakes in bedrock were analysed. The amplification power spectra and average spectra of all records were calculated. The seismic hazard analysis of 17 typical UHV converter stations was carried out, and the bedrock response spectra with exceedance probability of 10% and 2% in 50 years were proposed. The structural forms of the existing main response spectrum descending segments were compared and analysed. The corresponding response spectra of the long period strong earthquake records and the bedrock response spectra of the UHV converter station were fitted. The bedrock response spectrum of the UHV converter valves with the period range of 0-10s was determined, which lays a foundation for the seismic performance evaluation of the UHV converter valves.

Alternative approach in Partial Capacity Design (PCD) by using predicted post-elastic story shear distribution

The Capacity Design Method is an approach widely used to design earthquake resistant structures. It allows the structures to dissipate earthquake energy by forming plastic hinges through beam side sway mechanism. In the design process, the columns need to be designed stronger than the beams connected to them. Several previous studies have been conducted to propose alternative method allowing partial side sway mechanism namely the Partial Capacity Design (PCD) Method. In this method, selected columns are designed to remain elastic and the plastic hinges are allowed to occur only at the columns base. These columns are designed to resist increased forces. Despite of some successful attempts, PCD method still needs to be developed because sometimes the intended mechanism was not observed. This study proposes a new approach to improve the Partial Capacity Design (PCD) method. Symmetrical 6 and 10 story buildings with 7 bays are analyzed using seismic load for city of Surabaya. Structure behavior under non-linear static analysis is well predicted by this approach. However, under non-linear dynamic analysis, a few unexpected plastic hinges of elastic columns were observed at upper stories. But it should be noted that the earthquake used for performance analysis (maximum considered earthquake) is 50% larger than the one used for design (earthquake level corresponding to elastic design response spectrum).

Evaluation of Seismic Performance and Soil-Structure Interaction (SSI) for Piloti-Type Buildings considering Korean Geotechnical Conditions

Piloti-type structure is a popular architectural style consisting of only columns or minimum number of shear-resisting walls on the first floor. The large difference in lateral stiffness between the first and the upper floors makes the structure very vulnerable to earthquakes. Through the recent earthquakes in Gyeongju (2016) and Pohang (2017), due to such structural disadvantages, many damage cases have been reported, especially in low-rise piloti-type buildings with five stories or less. In this study, seismic soil-structure interaction (SSI) analysis is conducted on low-rise piloti-type buildings considering Korean geotechnical characteristics, and the effect is analytically evaluated. To achieve this goal, seismic SSI analysis applying the measured Gyeongju earthquake and design response spectrum (DRM) based on the architectural design codes are conducted by constructing three-dimensional structural analysis models with a five-story piloti-type building and four different soil properties: fill (FI), alluvial soil (AS), weathered soil (WS), and weathered rock (WR). From the analysis results, it is found that WS soil is largely affected by the seismic SSI, and the influence of the seismic SSI is different for each soil type regardless of the type of earthquake. Through the parameter study, simple and reasonable estimates are proposed to consider the SSI effect on the base shear in low-rise piloti-type buildings.

Study on the additional support length requirements of single-span bridges due to skew using a simplified method

Skew bridges with seat-type abutments are frequently unseated in earthquakes due to large transverse displacements at their acute corners. It is believed these large displacements are due to in-plane rotation of the superstructure. Lack of detailed guidelines for modeling of skew bridges, many current design codes give empirical expressions rather than theoretical solutions for the additional support length required in skew bridges to prevent unseating. In this paper, a parametric study has been carried out to study the influence of skew angle, aspect ratio and fundamental periods of bridges on the additional support length requirements of single-span bridges due to skew using a shake table experiment validated Simplified Method, which is capable of simulating gap closure based on response spectrum analysis. This method is developed based on the premise that the obtuse corner of the superstructure engages the adjacent back wall during lateral loading and rotates about this corner until the loading reverses direction. A design response spectrum specified in AASHTO LRFD Specifications was employed to represent the design-level earthquakes. The results show the additional length required to prevent unseating due to skew increases with the skew angle in an approximately linear manner when the angle is less than a critical value and decreases for angles above this value. This critical skew angle increases with the aspect ratio approximately in a linear manner and shows negligible dependence on the fundamental periods of the bridges, and combination of span length and width. In addition, the critical skew angle varies between 58° and 66°, when the aspect ratio is varied from 3.0 to 5.0. The results also show that the empirical formulas for minimum support length requirements of skew bridges in current codes and specifications can not accurately reflect the influence of skew.

Towards improving the seismic hazard map and the response spectrum for the state of RN/Brazil

Although Brazilian seismic activity is defined as low to moderate, it is known that intraplate earthquakes can also be associated to high intensities. In Brazil, the state of Rio Grande do Norte (RN) is one of the most seismically active areas, but there is no specific study to evaluate the seismic hazard in this region. This paper presents analyses towards improving the seismic hazard map, the peak ground acceleration value and the response spectrum of RN. The methodology is based on Probabilistic Seismic Hazard Analysis, comparing the results to the design criteria defined in the Brazilian code NBR 15421:2006 (Design of seismic resistant structures – Procedure). The analyses show that, in general, the code sets conservative values for the peak ground acceleration and for the design response spectrum; however, related to this last one, the shape is quite different.

Proposed Equations for Calculating Dynamic Hydraulic Pressure in a Rectangular Structure

When damaged by an earthquake, a general structure suffers only primary damage such as in the structure’s collapse, whereas a fluid storage structure can cause secondary damage such as environmental contamination or personal injury due to leakage of its internal fluid. In this study, the flow characteristics of fluid inside a fluid storage structure during an earthquake were analyzed, and an equation to calculate the dynamic hydraulic pressure of the fluid acting on the structure during an earthquake was proposed. The seismic load applied to the fluid storage structure was modified to satisfy the design response spectrum in 300 frequencies so that sufficient earthquake energy was obtained in any natural frequency of the fluid storage structure. In addition, the flow characteristics of the fluid inside the fluid storage structure were examined according to the shape change of the seismic wave and the ratio of the height of the fluid to the width of the fluid storage structure. A resulting equation for calculating the hydraulic pressure reflecting the fluctuation characteristics of the fluid was derived, and structural analysis was performed based on this equation and equations proposed by prior research to compare the member force and the hydraulic pressure in a dangerous section. As a result, it was confirmed that the equation proposed in this study showed similar values to previously proposed equations and could obtain fairly reliable results. Therefore, based on the proposed equation in this study, it is possible to calculate hydraulic pressure by reflecting the free-water surface fluctuation characteristics of fluid inside a fluid storage structure during an earthquake.

Response spectrum-based seismic response of bridge embankments

A single degree of freedom model is presented for calculating the free-field seismic response of bridge embankments due to horizontal ground shaking using equivalent linear analysis and a design response spectrum. The shear wave velocity profile, base flexibility, 2D shape, and damping ratio of the embankment are accounted for in the model. A step-by-step procedure is presented for calculating the effective cyclic shear strain of the embankment, equivalent homogeneous shear modulus and damping ratio, fundamental period of vibration, peak crest acceleration, peak shear stress profile, peak shear strain profile, equivalent linear shear modulus profile, and peak relative displacement profile. Model calibration and verification of the proposed procedure is carried out with linear, equivalent linear, and nonlinear finite element analysis for embankments with fundamental periods of vibration between 0.1 and 1.0 s. The proposed model is simple, rational, and suitable for practical implementation using spreadsheets for a preliminary design phase of bridge embankments.