Seismic response analysis of multiple-frame bridges with unseating restrainers considering ground motion spatial variation and SSI

Unseating damages of bridge decks have been observed in many previous major earthquakes due to large relative displacement exceeding the available seat length. Steel cable restrainers are often used to limit such relative displacements. Present restrainer design methods are based on the relative displacements caused by the different dynamic characteristics of adjacent bridge structures. However, the relative displacements in bridge structures are not only caused by different dynamic characteristics of adjacent bridge segments. Recent studies indicated that differential ground motions at supports of bridge piers and Soil Structure Interaction (SSI) could have a significant influence on the relative displacement of adjacent bridge components. Thus the present design methods could significantly underestimate the relative displacement responses of the adjacent bridge components and the stiffness of the restrainers required to limit these displacements. None of the previous investigations considered the effects of spatially varying ground motions in evaluating the adequacy of the restrainers design methods. Moreover, the code recommendation of adjusting the fundamental frequencies of adjacent bridge structures close to each other to mitigate relative displacement induced damages is developed based on the uniform ground motion assumption. Investigations on its effectiveness to mitigate the relative displacement induced damages on the bridge structures subjected to spatially varying ground motion and SSI are made. This paper discusses the effects of spatially varying ground motions and SSI on the responses of the multiple-frame bridges with unseating restrainers through inelastic bridge response analysis

Full-Scale Shaking Table Tests on a Substandard RC Building Repaired and Strengthened with Post-Tensioned Metal Straps

The effectiveness of a novel Post-Tensioned Metal Strapping (PTMS) technique at enhancing the seismic behaviour of a substandard RC building was investigated through full-scale shake-table tests during the EU-funded project BANDIT. The building had inadequate reinforcement detailing in columns and joints to replicate old construction practices. After the bare building was initially damaged significantly, it was repaired and strengthened with PTMS to perform additional seismic tests. The PTMS technique improved considerably the seismic performance of the tested building. Whilst the bare building experienced critical damage at an earthquake of PGA=0.15g, the PTMS-strengthened building sustained a PGA=0.35g earthquake without compromising stability

User's Manual for LZAK-C64, A Computer Program to Implement the Q-Model on Commodore 64

Report No. CCEER-84-1A simple nonlinear model (called the Q-Model) for seismic displacement history analysis of reinforced concrete plane frames was implemented on a Commodore 64. This manual presents a brief description of the model (see the Appendix) and outlines the procedure to use the model. It is assumed that the user is familiar with the derivation of the properties of the Q-Model. Two examples are presented to demonstrate the input preparation and the resulting output (Abstract by authors)

Experimental and Analytical Seismic Studies of a Four-Span Bridge System with Innovative Materials

Report No. CCEER-10-04As part of a multi-university project utilizing the NSF Network for Earthquake Engineering Simulation (NEES), a quarter-scale model of a four-span bridge incorporating plastic hinges with different advanced materials was tested to failure on the three shake table system at the University of Nevada, Reno (UNR). The bridge was the second test model in a series of three 4-span bridges, with the first model being a conventional reinforced-concrete (RC) structure. The purpose of incorporating advanced materials was to improve the seismic performance of the bridge with respect to two damage indicators: column damage and permanent deformations. The goals of the study presented in this document were as follows: 1. Evaluate the seismic performance of a 4-span bridge system incorporating SMA/ECC and built-in rubber pad plastic hinges as well as post-tensioned piers 2. Quantify the relative merit of these advanced materials and details compared to each other and to conventional reinforced concrete plastic hinges 3. Determine the influence of abutment-superstructure interaction on the response 4. Examine the ability of available elaborate analytical modeling techniques to model the performance of advanced materials and details 5. Conduct an extensive parametric study of different variations of the bridge model to study several important issues in bridge earthquake engineering The bridge model included six columns, each pair of which utilized a different advanced detail at bottom plastic hinges: shape memory alloys (SMA), special engineered cementitious composites (ECC), elastomeric pads embedded into columns, and post-tensioning tendons. The design of the columns, location of the bents, and selection of the loading protocol were based on pre-test analyses conducted using computer program OpenSees. The bridge model was subjected to two-horizontal components of simulated earthquake records of the 1994 Northridge earthquake. Over 340 channels of data were collected. The test results showed the effectiveness of the advanced materials in reducing damage and permanent displacements. The damage was minimal in plastic hinges with SMA/ECC and those with built-in elastomeric pads. Conventional RC plastic hinges were severely damaged due to spalling of concrete and rupture of the longitudinal and transverse reinforcement. Extensive post-test analytical studies were conducted and it was determined that a computational model of the bridge that included bridge-abutment interaction using OpenSees was able to provide satisfactory estimations of key structural parameters such as superstructure displacements and base shears. The analytical model was also used to conduct parametric studies on single-column and bridge-system response under near-fault ground motions. The effects of vertical excitations and transverse shear-keys at the bridge abutments on the superstructure displacement and column drifts were also explored

Non-Proprietary UHPC for Anchorage of Large Diameter Column Bars in Grouted Ducts

Report No. CCEER-19-03Accelerated bridge construction (ABC) is a bridge construction method that employs innovative construction techniques and can be applied in seismic or non-seismic regions of the nation to effectively reduce the onsite construction time. A non-coupled plunged, also referred to as precast column with no couplers (PNC), detail for column to footing and column to cap connections using ducts filled with ultra-high performance (UHPC) has been demonstrated as an effective connection for seismic applications. To expand the use of this ABC connection, a feasible and non-proprietary UHPC mix is crucial. The overall objective of this research is to develop a non-proprietary UHPC mix using locally available materials in the West, mainly from California and Nevada, that would reduce the UHPC cost and sole source problem without compromising the essential properties required for the grouted ducts ABC seismic connection. The study first presents an extensive literature review for high performance cement-based materials that most frequently used and locally available in the US market. The non-proprietary UHPC mix design process and material characterization is discussed next. Two sources of aggregates (Nevada and California) with two different characteristics were selected for the study. The aggregate from Nevada is a blended concrete sand that is 100% crushed. The aggregates from California is a concrete river sand that is uncrushed. The optimum gradation for dense aggregate packing and proportions of constituents were selected based on 28-day compressive strengths and flow characteristics of the mix. It was found that the aggregate gradation with fineness modulus less than 3.0 meets the minimum 28-day compressive strength criteria of 12 ksi and flow of 10 in. The 28-day compressive strength of the mix developed using river sand aggregates from California, designated as UNR-UHPC-A, and the mix developed using 100% crushed aggregates from Nevada, designated as UNR-UHPC-B, was found to be 15 ksi and 14 ksi, respectively as measured using 4-in-by 8-in cylinders. The non-proprietary UHPC mixes were further evaluated for flexural and direct tensile strength properties after meeting the minimum compressive strength and flow criteria. A major part of this study used the finalized UHPC mix designs from both sources of aggregates to evaluate grouted ducts anchorage behavior using 22 full-scale tests with #10 rebars. Several parameters were varied to evaluate the effect of embedment depth, single versus bundled rebars, duct sizes, and duct material. Moreover, the tests also compared the anchorage behavior of the developed mixes with the commercially available UHPC and standard grouts; the other alternatives in such connections. All rebars were eccentrically placed into the ducts to emulate more practical field and worst case conditions. Based on the tests results, development length equations of rebars eccentrically placed in galvanized steel corrugated ducts filled with UHPC have been revised and presented

User's Manual of ISADAB and SIBA, Computer Programs for Nonlinear Transverse Analysis of Highway Bridges Subjected to Static and Dynamic Lateral Loads

Report No. CCEER-86-2This document presents the user's manual for two computer programs for the nonlinear analysis of highway bridges subjected to horizontal forces. The programs are called ISADAB and SIBA. The former was developed in FORTRAN IV on a CYBER 730 mainframe and performs a variety of tasks ranging from static to earthquake analysis of bridges. The latter consists of a package of three programs which were developed in BASIC on a Commodore 64. The SIBA package is for only static nonlinear analysis of bridges and for the related graphical displays (Abstract by authors)

CCEER-20-08: Seismic Response Of Precast Columns With Non-Proprietary UHPC-Filled Ducts Abc Connections

Report No. CCEER 20-08Accelerated bridge construction (ABC) has several advantages, such as reducing onsite construction time, reducing the traffic congestion around construction sites, and improving the quality of the prefabricated elements for both new bridges or rehabilitation or replacement of old bridges. ABC is considered a good and efficient candidate to replace the cast-in-place (CIP) conventional on-site construction techniques. ABC has been widely used in low seismic regions mostly in the superstructure elements. However, ABC is not widely implemented in the substructure elements such as column-base connections, especially in moderate and high seismic regions due to the uncertainty in the seismic performance of the substructure connections. Few ABC seismic connections were developed and have been demonstrated for potential use in high seismic regions. Among these is ultra-high performance concrete (UHPC) filled grouted-duct connection. The use of proprietary UHPC poses another challenge for wider implementation of this type of connection. The overall goal of this study was to develop non-proprietary, feasible alternative for the grouted-duct ABC seismic connection for precast bridge columns that can emulate the seismic performance of conventional CIP connections. Reducing the costs and using non-proprietary materials was the focus of this study to establish a less expensive, less restrictive alternative for UHPC-filled grouted-duct connections and avoid sole-source specification. In the first phase of this project and a companion study (Subedi et al. 2019), several non-proprietary UHPC mixes were developed and two were selected at the University of Nevada, Reno. They were used in 22 large scale pullout specimens to determine the bond behavior of UHPC-filled duct systems. Given their observed satisfactory performance, one of the non-proprietary UHPC mixes was further used and incorporated into UHPC-filled duct connections of two 42%-scale column models to connect the precast columns to footings. Both column models were tested to failure under combined axial and cyclic lateral loading to investigate their seismic performance and evaluate their ability to emulate the seismic performance of the CIP system. Moreover, analytical investigation for each column model was conducted to simulate the global response of the column models. The analytical studies were conducted using finite element computer program OpenSEES. Specific modeling assumptions for these connections that include the bond-slip effects in bars and ducts and bar debonding effects were validated for future implementation and further use in the design of this connection in actual bridges. Overall, non-proprietary UHPC-filled duct connections were successfully demonstrated to have acceptable seismic performance and are, in turn, recommended as suitable precast column-to-footing or column-to-cap beam connections for moderate and high seismic regions. Using such connection with the proposed UHPC mix can assure the formation of full plastic moment in columns without any connection damage

Seismic Response of Bridge Pier Walls in the Weak Direction

Report No. CCEER-99-3The research presented in this report consisted of an experimental and an analytical study. The objective of the experimental study was to evaluate the out-of-plane seismic behavior of representative bridge pier walls that exist in the US. The analytical study had two objectives, the first was to develop and calibrate an analytical model to determine the seismic response of bridge pier walls, while the second was to develop an approach that relates the displacement ductility capacity to the amount of confinement steel. A comprehensive bridge pier wall survey was conducted to collect information about existing typical pier walls in the US. The data were well distributed geographically and states with full range of seismicity were represented. A statistical analysis was performed on the collected data to select test parameters and specimens. Seven specimens were designed, built, and tested in the experimental study under slow cyclic loads. The failure mode of the wall specimens was either compression failure of the concrete or fracture of the vertical reinforcing bars due to low-cycle fatigue. An analytical model was developed and calibrated. A computer program called "PIER" was written to implement the analytical model. Good agreement was found when comparing the calculated and measured responses of the pier wall specimens tested in the course of this study and at the University of California at Irvine (UC-Irvine). A parametric study was conducted to extend the seismic response study to bridge pier wall cases that were not tested experimentally using the computer program "PIER". The parameters were the ratio of the wall height to thickness, the vertical steel ratio, the confinement steel ratio, and the axial load index. Pier wall cases that need retrofit were identified based on the expected seismic response. A new practical approach to relate the confinement reinforcement in the plastic hinge zones of bridge pier walls to the displacement ductility capacity was developed based on the results of the parametric study. The proposed approach is recommended for design because, unlike other available models that are based on testes of columns, the proposed model is calibrated against wall data. The displacement ductility capacity of six typical pier walls that contained confinement steel designed using the available code provisions was calculated using the proposed approach. A comparison of the resulting ductilities was made to identify design provisions that lead to best level of performance. The displacement ductility capacity of pier walls 29 and 30 in Moribe Viaduct that was severely damaged during the 1995 Hanshin Awaji Earthquake, Japan, was calculated. The damage and the poor seismic performance of these walls, indicated that the actual ductility capacity was lower than those calculated. The likely reason for the poor seismic performance of the walls was discussed