Lawrence D. Reaveley

Performance-based design using structural optimization

A new methodology for seismic design is proposed based on structural optimization with performance-based constraints. Performance-based criteria are introduced for the seismic design of new buildings. These criteria are derived from the National Guidelines for Seismic Rehabilitation of Buildings (Reference [19], Federal Emergency Management Agency (FEMA), ‘NHERP Guidelines for seismic rehabilitation of buildings’, Report Nos 273 and 274, Washington, DC, 1997) for retrofitting existing structures. The proposed design methodology takes into account the non-linear behaviour of the structure. The goal is to incorporate in the design the actual performance levels of the structure, i.e. how much reserve capacity the structure has in an earthquake of a given magnitude. The optimal design of the structure minimizes the structural cost subjected to performance constraints on plastic rotations of beams and columns, as well as behavioural constraints for reinforced concrete frames. Uncertainties in the structural period and in the earthquake excitation are taken into account using convex models. The optimization routine incorporates a non-linear analysis program and the procedure is automated. The proposed methodology leads to a structural design for which the levels of reliability (performance levels) are assumed to be quantifiable. Furthermore, the entire behaviour of the structure well into the non-linear range is investigated in the design process. Copyright

Performance-Based Evaluation of Reinforced Concrete Building Exterior Joints for Seismic Excitation

Beam-column joints of nonductile reinforced concrete buildings that were built prior to the current seismic code provisions have been investigated using several performance-based criteria. Four half-scale reinforced concrete exterior joints were tested to investigate their behavior in a shear-critical failure mode. The joints were subjected to quasi-static cyclic loading, and their performance was examined in terms of lateral load capacity, drift ratio, axial load reduction in the column at high drift ratios, joint shear strength, ductility, shear deformation angle of the joint, and residual strength. Two levels of axial compressive column load were investigated to determine how this variable might influence the performance of the joint. Specific performance levels for this type of reinforced concrete joint were established and a comparison was made to current design and rehabilitation standards. A limit states model was established, which could be used for performance evaluation or seismic rehabilitation.

Axial Load Behavior of Concrete Columns Confined with GFRP Spirals

The writers evaluated the confinement that was provided by glass fiber-reinforced polymer (GFRP) spirals in concrete columns under axial load. Given that GFRP spirals are resistant to chloride-induced corrosion, the option of replacing steel spirals with GFRP spirals was explored to determine whether this would reduce the corrosion of the vertical steel bars in hybrid columns. The writers investigated the axial load behavior of 10 spirally reinforced concrete columns. Six of the 254-mm diameter columns were confined with a GFRP spiral and four were confined with a steel spiral. Some of the columns that were confined with a GFRP spiral utilized steel vertical bars (hybrid columns), whereas others utilized GFRP vertical bars (all-GFRP columns). The stress-strain and load-displacement behavior of all columns was studied. Analytical expressions predicted the axial load capacity of the hybrid and all-GFRP-reinforced concrete columns. Axial compression tests of all-steel-reinforced and hybrid specimens subjected to accelerated corrosion were also carried out. The latter exhibited a smaller corrosion rate, similar axial load capacity, and equal or higher ductility relative to steel corroded columns.

In‐Situ Verification of Rehabilitation and Repair of Reinforced Concrete Bridge Bents under Simulated Seismic Loads

Three in-situ tests were performed on two bents of a reinforced concrete (RC) bridge under quasi-static cyclic loads. The bridge was built in 1963 and did not possess the necessary reinforcement details for ductile performance. The tests included an as-built bent, a bent rehabilitated with carbon fiber reinforced polymer (FRP) composite jackets, and a damaged bent repaired with epoxy injection and carbon FRP composite jackets. Two new concepts of strengthening bridge bents with FRP composites were implemented in this study. The first involves shear strengthening and confinement of a beam cap-column joint through an FRP composite “ankle-wrap.” The second is an FRP composite “U-strap” to improve the anchorage of column longitudinal steel reinforcement extending into the joint. FRP composite jackets were also implemented in the columns and beam cap. An additional rehabilitation measure was that of anchorage of the piles to the pile cap using epoxied high strength steel bars. The performance of the bent in the as-built condition and that of the rehabilitated and repaired bents is described in terms of strength, stiffness, displacement ductility, and energy dissipation.

Seismic Strengthening of Reinforced-Concrete Multicolumn Bridge Piers

The analysis, seismic rehabilitation measures, and in-situ performance of a reinforced-concrete (RC) bridge pier subjected to quasi-static loads are presented. The bridge was built in 1963 and was designed for gravity and wind but not seismic loads. The reinforcement details are compared with AASHTO requirements for seismic zones 3 and 4. The bridge pier was rehabilitated with steel dowels connecting the piles to the pile caps and RC grade beam connecting the three pile caps; carbon Fiber-Reinforced-Polymer (FRP) composite jackets were used to rehabilitate the columns, cap beam, and T-joints. An analytical model is presented that includes the effects of soil-pile-structure interaction and the seismic rehabilitation measures. Critical events in the experimental performance of the bridge pier are identified. Comparisons are made between the piers performance and that of other piers tested in situ at the same site that were rehabilitated with incremental measures.

Earthquake Damage and Loss Estimation Methodology and Data for Salt Lake County, Utah (ATC‐36)

As a follow on to the Applied Technology Council (ATC) project to develop earthquake damage evaluation data for California (ATC-13 project), ATC has conducted a project to update and translate the ATC-13 data and methodology for use in Salt Lake County, Utah (ATC-36 project). Methodology has been developed and/or updated for: (1) estimation of damage due to ground shaking, (2) estimation of damage due to collateral loss causes such as fault rupture, ground failure, inundation, and fire following earthquake, (3) estimation of time to restore damaged facilities to pre-earthquake usability, and (4) estimation of deaths and injuries. In addition, an electronic inventory of approximately 200,000 structures (buildings and lifeline systems) within Salt Lake County has been developed. The data and methodology have been developed for implementation in a geographic information system (GIS) application, or in a non-GIS software application, such as a relational database management system or spreadsheet.

Experimental Evaluation of Slender High-Strength Concrete Columns with GFRP and Hybrid Reinforcement

AbstractThe behavior of slender high-strength concrete columns reinforced with glass fiber-reinforced polymer (GFRP) bars and spirals subjected to concentric and eccentric axial loads was evaluated. Large-scale tests were conducted for nine circular concrete columns (three short and six slender) reinforced with internal GFRP-spirals and either steel, GFRP, or a combination of steel and GFRP longitudinal bars. The short and slender columns had slenderness ratios equal to 10 and 49, respectively. Axial load tests were conducted with loads placed concentrically (short columns) and at two eccentricities (slender columns) to observe the general behavior associated with different geometric and loading conditions. The behavior of slender columns with small eccentricity (8.3% of the column size) was governed by material failure, while that of slender columns with large eccentricity (33% of column size) was governed by a buckling failure. The research shows that GFRP spirals and GFRP longitudinal bars are a viable...

NEHRP Guidelines and Commentary for the Seismic Rehabilitation of Buildings

Based on the conclusion that the primary barrier to widespread seismic rehabilitation of buildings in the United States was the lack of a consensus-backed, nationally applicable, professionally accepted rehabilitation standard, the Federal Emergency Management Agency supported the development of the NEHRP Guidelines and Commentary for the Seismic Rehabilitation of Buildings (FEMA 273 and 274). A six-year effort by a team of experienced professional practitioners and university researchers who were motivated to produce a standard that specifically addressed the differences in designing for seismic resistance in new buildings, as opposed to existing buildings, resulted in the NEHRP Guidelines and Commentary for the Seismic Rehabilitation of Buildings. These NEHRP Guidelines will provide the tools for design professionals of varying expertise in seismic design to design economical and appropriate seismic rehabilitation for buildings of essentially any size, commonly used building material and configuration.

Repair of Prestressed Concrete Beams with Damaged Steel Tendons Using Post-Tensioned Carbon Fiber- Reinforced Polymer Rods

Research implementing unibody clamp anchors and a simple mechanical stressing device to post-tension external, unbonded carbon fiber-reinforced polymer (CFRP) rods is presented. The experiments described in the paper concern three prestressed concrete beams: one was used as the control beam and the other two were damaged. Damage consisted of cracked concrete that was removed and internal steel tendons that were cut to simulate vehicle collision, corrosion, or both. The repair system was then applied to the two damaged concrete beams. The CFRP repair system performed well, increasing the ultimate strength and flexural capacity of the damaged beams to meet or exceed the strength capacity of the control. An analytical model considering the tendon stress at ultimate and the distribution of internal forces was developed to explore design recommendations for the use of the unibody clamp anchors and stressing device for post-tensioning CFRP rods.

Behavior of R/C Bridge Bent with Grade Beam Retrofit under Simulated Earthquake Loads

Results from an in-situ lateral load test of a reinforced concrete bridge bent, whose design was inadequate under current seismic codes are presented. Details of a reinforced concrete grade-beam seismic retrofit design are provided. A nonlinear analysis model including soil-structure interaction predicted the experimental results with reasonable accuracy. Structural displacement ductility and that resulting from bent cap and foundation flexibility were compared to theoretical relations. Limiting strains and stresses for reinforcement in columns, bent-cap column joints, lap splices, and pile-cap column joints were measured and compared to the literature. Comparison of the experimental column plastic hinge length to predictive relationships shows that the latter slightly underestimate the measured plastic hinge length. Damage indices based on energy were used to evaluate the performance. Comparison with a test of a bridge bent without a grade beam retrofit shows that the foundation seismic retrofit was successful in enhancing the performance of the system.