This is to confirm that the thesis entitled "APPLICATION OF PUSHOVER ANALYSIS TO RC BRIDGES" submitted by Mr. Kaliprasanna Sethy in partial fulfillment of the requirements for the award of a Master of Technology Degree in Civil Engineering with specialization in Structural Engineering at the National Institute of Technology Rourkela is an authentic work done by him under my supervision. The satisfaction and euphoria of successful completion of any task would be incomplete without the mention of the people who made it possible, whose constant guidance and encouragement crowned my efforts with success.
Panda, Head of Civil Engineering Department, for all the facilities provided for the successful completion of this work. I am also very grateful to all the faculty members of the department, especially the construction major for their constant encouragement, invaluable advice, encouragement, inspiration and blessings during the project. In order to solve this problem, the aim of this project was to perform a case study of seismic evaluation for an existing AB bridge using nonlinear static (pushover) analysis.
Therefore, push-through analysis with single load pattern cannot provide correct results for a bridge model. Standard pushover analysis using FEMA displacement coefficient method and an improved upper limit pushover analysis method were used to analyze the building. The evaluation results presented here show that the selected bridge does not have the capacity to achieve any of the desired performance levels.
SAP Structural Analysis Program SDOF Single Degree of Freedom SPA Standard Pushover Analysis TLP Triangular Load Pattern.
CHAPTER-1
INTRODUCTION
INTRODUCTION
- BACKGROUND
- OBJECTIVES
- METHODOLOGY
The northeastern region of the country and the entire Himalayan belt are prone to large earthquakes of magnitude greater than 8.0. Many efforts were also focused on the need to enforce legislation and make constructors and builders responsible for the safety of structures under seismic loads. The magnitude of the seismic design forces has been significantly improved overall, and the seismic zoning of some regions has also been improved.
In order to solve this problem, the objective of this work is to conduct a case study of seismic evaluation for an existing AB bridge using nonlinear static (pushover) analysis. So, in this study, the improved thrust analysis is also used to verify the results. Conduct a detailed case study of thrust analysis of a reinforced concrete bridge using standard thrust analysis and other improved thrust analyses.
A thorough literature review to understand the seismic evaluation of building structures and the application of pushover analysis. The first part of Chapter 2 discusses details about pushover analysis procedures according to FEMA 356 and several improvements to this procedure available in the literature.
CHAPTER-2
LITERATURE REVIEW
- GENERAL
- PUSHOVER ANALYSIS
- Pushover Analysis Procedure
- Lateral Load Patterns
- Target Displacement
- SHORT COMINGS OF STANDARD PUSHOVER ANALYSIS
- ALTERNATE PUSHOVER ANALYSIS PROCEDURES
- APPLICATION OF PUSHOVER ANALYSIS TO RC BRIDGES
- SUMMARY
The use of non-linear static analysis (thrust analysis) came into practice in the 1970s, but the potential of thrust analysis has only been recognized in the last 10-15 years. The target displacement is the maximum displacement (elastic and inelastic) of the building on the roof expected under the selected seismic ground motion. Pushover analysis is a static non-linear procedure in which the magnitude of the lateral load increases monotonically while maintaining a predetermined pattern of height distribution.
The analysis results are sensitive to the selection of the control node and the selection of the lateral loading pattern. In general, the center of mass on the roof of the building is considered the control node. In the pushover analysis, the building is pushed with a specific load distribution pattern over the height of the building.
Although inertial force distributions vary with earthquake severity and with time, FEMA 356 recommends a largely invariant load model for pushover analysis of frame buildings. A vertical distribution proportional to the shape of the fundamental mode in the direction under consideration (allowed only when more than 75% of the total mass participates in this mode). iii). A vertical distribution proportional to the cross section distribution of the story calculated by combining the modal responses from an analysis of the building response spectrum (sufficient number of modes to capture at least 90% of the total mass of the building required to be considered).
This is a very important parameter in pushover analysis because the global and component response (forces and displacement) of the building at the target displacement is compared to the desired performance limit state to know the performance of the building. C0 = a form factor (often taken as the first mode participation factor) to convert the spectral displacement of equivalent SDOF system to the displacement at the building roof. This equation does not depend on the decaying characteristics of the hysteretic behavior of the system.
It depends only on the displacement ductility ratio (μ) and the post-yield stiffness ratio (α) of the inelastic system. Important approaches lie in the choice of the lateral loading pattern and in the calculation of the target displacement. The method, as prescribed in FEMA 356, ignores the contribution of the higher modes to the overall response.
This degradation leads to changes in the period and modal characteristics of the structure, which affect the load generated during seismic ground motion. e). The vertical component of the seismic load is neglected; this can be important in some cases.
CHAPTER-3
STRUCTURAL MODELLING
STRUCTURAL MODELLING
- INTRODUCTION
- COMPUTATIONAL MODEL
- Material Properties
- Structural Elements
- BRIDGE GEOMETRY
- MODELLING OF FLEXURAL PLASTIC HINGES
- Stress-Strain Characteristics for Concrete
- Stress-Strain Characteristics for Reinforcing Steel
- Moment-Rotation Parameters
- SUMMARY
The traffic is placed on the head of the concrete pier through the bearing and is closed in the transverse direction. In implementing the pushover analysis, the model must take into account the nonlinear behavior of the structural elements. In the present study, a point plasticity approach is considered for modeling the nonlinearity, where the plastic hinge is assumed to be centered at a specific point of the frame part under consideration.
The flexural hinges in this study are defined by moment-rotation curves calculated based on the cross-section and reinforcement details at the possible hinge locations. The stress-strain curve of concrete in compression forms the basis for the analysis of any reinforced concrete section. The characteristic and design stress-strain curves specified in most design codes (IS BS 8110) do not really reflect the actual stress-strain behavior in the post-peak region, as it (for ease of calculation) assumes a constant stress in this region (strains between 0.002 and 0.0035).
In reality, as shown by experimental testing, the post-peak behavior is characterized by a decreasing branch, which is attributed to 'softening' and micro-cracking in the concrete. However, the stress-strain relationship specified in ACI 318M-02 considers some of the important features from actual behavior. Therefore, this model is chosen in the present study to calculate the hinge properties.
A single equation defines the stress-strain curve (both ascending and descending branches) in this model. The model can be applied to any shape of the section of the concrete part bounded by any type of transverse reinforcement (spirals, transverse links, circular or rectangular hoops). The Code-specified 'characteristic' and 'design' stress-strain curves for grade Fe-415 reinforcing steel (in tension or compression) are shown in Figs.
Moment-rotation parameters are the actual input for modeling the hinge properties and these can be calculated based on the moment-curvature relationship. It is usually limited to 20% of the yield point, and the ultimate rotation, θu, can be included. This chapter presents details of the basic modeling technique for the linear and nonlinear analyzes of RC framed structures.
CHAPTER-4
RESULTS AND DISCUSSIONS
RESULTS AND DISCUSSIONS
INTRODUCTION
MODAL PROPERTIES
PUSHOVER ANALYSIS
- Target Displacements
For UBPA, the load pattern for the analysis was calculated from the modal properties as discussed in Section 2.4.1. Capacity curve of the bridge as obtained from the two thrust analyzes (FEMA 356 with triangular load pattern and UBPA) is plotted and shown in Fig. This figure demonstrates the influence of load pattern on the capacity curve of the structure.
Target displacements were calculated for different performance levels according to the procedures discussed in Chapter 2. The results obtained from Pushover Analysis (both for FEMA-356 and UBPA) show that the bridge collapses before the Target Displacement is reached. For FEMA-356, the failure is concentrated in the center of the bridge, while, for UBPA, the failure is distributed along the length of the bridges.
Since the bridge could not achieve the target displacement in any of the pushover cases, it can be concluded that the bridge is not safe for any performance limit state under the seismic demand corresponding to zone V. The distribution of the hinges is different for the two pushover analyzes performed in this study. For FEMA-356 loading hinges are concentrated in the center of the bridges For UBPA loading the hinges are distributed over the entire length of the bridge.
CHAPTER-5
SUMMARY AND CONCLUSIONS
SUMMARY AND CONCLUSIONS
SUMMARY
CONCLUSIONS
Therefore, it requires readjustment. ii) The distributions of the hinges are different for the two pushover analyzes performed in this study.
Application of Thrust Analysis for AB Bridges Modal Thrust Analysis Procedure for Estimating Seismic Demands for Buildings with Unsymmetrical Design. Evaluation of a Modified MPA Procedure Assuming Higher-than-Elastic Modes for Estimating Seismic Demands”. 2005) “Probabilistic assessment of seismic movements in reinforced concrete buildings”. Adaptive spectra-based pushover procedure for seismic evaluation of structures”. 2004) “Evaluation of Modal Analyzes and FEMA Pushover Analyses: SAC Buildings”.
Indian Standard for Plain and Reinforced Concrete – Code of Practice”, Bureau of Indian Standards, New Delhi. Indian Standard Criteria for Earthquake Resistant Design of Structures”, Bureau of Indian Standards, New Delhi.
