Stress Response and Damage Characteristics of Local Members of a Structure due to Tunnel Blasting Vibrations Based on the High-Order Local Modal Analysis

Xiaoming Guan,Fei Zhao,Chunwei Zhang,Ben Mou,Yiming Ge

doi:10.1155/2019/7075024

Abstract

Damage characteristics and dynamic stress response of aging masonry structures for blast-induced ground motion were performed using high-order local modal analysis method. A complete investigation of damage types and locations of aging masonry buildings due to tunnel blasting vibration were performed by on-site survey. A typical 2-storey aging masonry building located above a tunnel was selected for dynamic response analysis. The experimental dynamic characteristics of the structure were determined by using the operational modal analysis (OMA) method. Finite element models for the masonry structures were updated by modifying material parameters based on OMA results. The first five natural frequencies of the updated finite element models ranged from 8.80–24.99 Hz, and the first five modes were global modes. The sixth to twentieth natural frequencies ranged from 26.10–36.34 Hz, and the sixth to twentieth modes were local modes whose deformation was greater than the global deformation. Since the principal frequencies of the tunnel blast vibration were mostly higher than the natural global modes’ frequencies and were much closer to the natural frequencies of local members, local members experienced more intensive vibrations compared to the main body structure. The principal compressive stress (PCS) and principal tensile stress (PTS) of local members were several times greater than that of the main body structure. Therefore, local members of the masonry building suffered most from the tunnel blasting vibration. Corners due to stress concentration, the contact area between brick and concrete, local members, and precast floor seams are prone to damage during tunnel blasting. With the vibration velocity increasing, the PCS and PTS of local members gradually increase. But, the PTS ratio of local members decreases with the increase of peak particle velocities. The dynamic response analysis result and the damage locations using high-order local modal analysis method are in accordance with the damage found at the site.

Highlights

Nowadays, with the remarkable progress of railways, highways, and subways, there is an increasing number of shallow buried tunnels being built beneath buildings in old urban districts
The stress response of the structure to vibrations during tunnel blasting was studied based on the modal analysis method, the operational modal analysis (OMA) test, and model updating of the structure, modal analyses of local members of the building and interaction between external blast vibration frequency and structural modes had not been investigated in the paper [13]
(2) If the dominant external ground motion frequencies are close to local mode natural frequencies, members will vibrate in those local modals and appear to have different deformation

Summary

Introduction

With the remarkable progress of railways, highways, and subways, there is an increasing number of shallow buried tunnels being built beneath buildings in old urban districts. The stress response of the structure to vibrations during tunnel blasting was studied based on the modal analysis method, the OMA test, and model updating of the structure, modal analyses of local members of the building and interaction between external blast vibration frequency and structural modes had not been investigated in the paper [13]. E dynamic response of local members of masonry structures under blast-induced ground excitations is examined using the updated finite element models. A complete investigation of damage types and locations of masonry buildings due to tunnel blasting vibration is performed by on-site survey. Because of use of concrete to grout seal between prefabricated floors without steel connection, it leads to a weak connection between each precast floor section Because of this weak connection and stiffness mutation, joints between prefabricated floors are prone to cracking under tunnel blasting vibration. The finite element model, which represents the actual dynamic characteristics of the masonry structure, is established and updated based on the results of the OMA test

Analytical Modal Analyses of the Masonry Building

OMA Test and Model Updating of the Structure

Dynamic Response of Local Members of the Masonry Building

Findings

Main structure