Sri Sritharan

Modeling of Strain Penetration Effects in Fiber-Based Analysis of Reinforced Concrete Structures

Focusing on the member end rotation due to strain penetration along reinforcing bars fully anchored in footings and bridge joints, this paper introduces a hysteretic model for the reinforcing bar stress versus slip response. This model can be integrated into fiber-based analysis of concrete structures using a zero-length section element. The authors demonstrate the ability of the proposed hysteretic model to capture the strain penetration effects by simulating the measured global and local responses of two concrete columns and a bridge T-joint system. Findings show that the analysis of concrete structures will appreciably underestimate the local response parameters that are used to quantify structural damage unless the strain penetration effects are satisfactorily modeled.

ANALYTICAL MODELLING OF THE SEISMIC BEHAVIOUR OF PRECAST CONCRETE FRAMES DESIGNED WITH DUCTILE CONNECTIONS

Pure precast beam-column systems incorporate unbonded reinforced at the critical sections, causing strain incompatibility between steel and concrete. As a result, classical section analysis method, well know for characterising monolithic concrete members, cannot be directly applicable to these systems. This paper provides a section analysis method suitable for precast members, incorporating, through an analogy with equivalent cast-in-place solution named “monolithic beam analogy”, an additional condition on the member global displacement. The proposed method was first validated with the experimental data from tests on beam-column Hybrid subassemblages. Using appropriate hysteresis rules and the response envelopes defined by the section analysis method, a prediction of the behaviour of the PRESSS test building was carried out. Satisfactory agreements obtained between the analytical and experimental results confirm the validity of the suggested methodology. Derivation of the method and experimental validation are herein presented.

Understanding Poor Seismic Performance of Concrete Walls and Design Implications

The 2010–2011 Canterbury earthquakes in New Zealand revealed (1) improved structural response resulting from historical design advancements, (2) poor structural performance due to previously identified shortcomings that had been insufficiently addressed in design practice, and (3) new deficiencies that were not previously recognized because of premature failure resulting from other design flaws. This paper summarizes damage to concrete walls observed in the February 2011 Christchurch earthquake, proposes links between the observed response and specific design concerns, and offers suggestions for improving seismic design of walls in the following areas: amount of longitudinal reinforcement in wall end regions, suitable wall thickness to minimize the potential for out-of-plane buckling, and minimum vertical reinforcement requirements.

Pile Setup in Cohesive Soil. I: Experimental Investigation

AbstractPile setup in cohesive soils has been a known phenomenon for several decades. However, a systematic field investigation to provide the needed data to develop analytical procedures and integrate pile setup into the design method rarely exists. This paper summarizes a recently completed field investigation on five fully instrumented steel H-piles embedded in cohesive soils, while a companion paper discusses the development of the pile setup method. During the field investigation, detailed soil characterization, monitoring of soil total lateral stress and pore-water pressure, collection of pile dynamic restrike data as a function of time, and vertical static load tests were completed. Restrike measurements confirm that pile setup occurs at a logarithmic rate following the end of driving, and its development correlates well with the rate of dissipation of the measured pore-water pressure. Based on the field data collected, it was concluded that the skin friction component, not the end bearing, contrib...

Effects of Seasonal Freezing on Bridge Column–Foundation–Soil Interaction and Their Implications

Several seismic regions around the world experience seasonal freezing that can drastically alter the soil-foundation-structure interaction and structural response under earthquake loads. This paper analytically investigates the effects of seasonal freezing on lateral load response of a bridge column supported by a cast-in-drilled-hole (CIDH) foundation shaft. Accounting for the temperature effects on materials, the analyses were conducted at ambient temperatures of 23°C, −1°C, −7°C, −10°C, and −20°C, and the results obtained at 23°C and −10°C were validated using experimental data. In comparison to the response at 23°C, the response of the column-shaft system in the range of −1°C to −20°C exhibited 40%–188% increase in the effective elastic stiffness, 17%–63% reduction in the lateral displacement capacity, 0.54–0.82 m upward shift in the maximum moment location, 25%–30% increase in the column shear demand, and 25%–80% increase in shear and 19%–68% reduction in the length of the plastic region in the CIDH shaft.

Current Design and Construction Practices of Bridge Pile Foundations with Emphasis on Implementation of LRFD

The Federal Highway Administration (FHWA) mandated the use of the load and resistance factor design (LRFD) approach in the U.S. for all new bridges initiated after September 2007. This paper presents the bridge deep foundation practices established through a nationwide survey of more than 30 DOTs in 2008. Highlighted by this study are the benefits of the LRFD as well as how the flexibility of its usage is being exploited in design practice. The study collected information on current foundation practice, pile analysis and design, pile drivability, pile design verification, and quality control. Since this is the first nationwide study conducted on the LRFD topic following the FHWA mandate, the status on the implementation of LRFD for bridge foundation design was also examined. The study found that: (1) more than 50% of the responded DOTs are using the LRFD for pile design, while 30% are still in transition to the LRFD; and (2) about 30% of the DOTs, who use the LRFD for pile foundations, are using regionally calibrated resistance factors to reduce the foundation costs.

Nonlinear finite element analyses of concrete bridge joint systems subjected to seismic actions

Following widespread damage to bridge joints in the San Francisco region from the 1989 Loma Prieta earthquake, the necessity for establishing an alternative method for seismic design of bridge joints was identified. Recognizing that conventional joint design practice based directly on shear forces results in congested reinforcement details, which are difficult to implement in practice, a rational design procedure was sought through large-scale testing of bridge joint systems and subsequent finite element and strut-and-tie analyses. The finite element part of the study is presented in this paper, which focuses on (a) identification of compression force flow and thus the load path across the joint, (b) examination of an efficient joint force transfer model, and (c) influence of cap beam prestressing. Combining the experimental and analytical results, a joint design method has been established in which reduction of joint reinforcement was achieved by treating joint shear as part of the complete force transfer across the joint, rather than as an independent action. The proposed design approach has been validated in a laboratory test on a full-scale multiple-column bridge bent.

SEISMIC DESIGN AND EXPERIMENTAL VERIFICATION OF CONCRETE MULTIPLE COLUMN BRIDGE BENTS

In the aftermath of widespread bridge damage in recent California earthquakes, a significant amount of research has been conducted to improve seismic performance of bridge structures. Compiling recent advances, 2 large-scale concrete multiple-column bridge bents were designed and subjected to simulated earthquake loading at the University of California-San Diego. In addition to serving as proof-test specimens, the bridge bents facilitated examination of improved cap beam-to-column joint reinforcement details to minimize construction problems. The design of the joints in the 1st test unit was simplified by using prestressing in the bent cap and examining the force transfer across the joint, which also enabled introduction of precast construction for concrete multiple column bents. In the 2nd test unit, joint reinforcement was minimized by utilizing efficient joint force transfer models and special reinforcement products. Design details, seismic performance, and selected test results are discussed.

Cyclic response of reinforced concrete walls with different anchorage details: Experimental investigation

Previoustestsofstructuralwallshaveroutinelyusedcontinuousreinforcementextendingfromthefoundationtothetopofthespec- imen. This detailing is consistently different from that of multistory walls in the field, which incorporate splices in the wall longitudinal rein- forcement above the wall-foundation interface. As a result, the performance of walls incorporating continuous reinforcement in the laboratory may not be representative of walls in the field that use lap splices or mechanical couplers near the wall base. This paper investigates lateral load behavior of three nominally identical structural walls with continuous reinforcement, lap splices, and mechanical couplers in the plastic hinge region, and quantifies the differences in their responses using force-displacement response, lateral deformation components, and energy dissipation estimated using equivalent viscous damping. DOI: 10.1061/(ASCE)ST.1943-541X.0000732.

Lessons Learned from Seismic Analysis of a Seven-Story Concrete Test Building

A uniaxial shake table test of a full-scale slice of a seven-story reinforced concrete wall building was performed at the University of California, San Diego. A 2D analytical model that primarily employed fiber-based beam-column elements was used for a blind prediction of the global response of the building to the imposed input accelerations. An improved analytical model, which adequately simulates the buildings dynamic response and comparison of measured and analytical results, is presented. The lessons learned from participation in the blind prediction with particular attention to the effects of issues commonly ignored in analytical modeling of concrete buildings are included.