Next-generation smart bridge pier foundation structure based on damage control design concept

Размещено на http://www.allbest.ru/

Next-generation smart bridge pier foundation structure based on damage control design concept

Hassan Muhammad Mahmood Ul, graduate student, Faculty of Engineering, Hokkaido University

Abstract

Pier is considered to be a key member in the bridge structure as it has to transfer to the superstructure loads to the foundation safely. However, there is always a high risk of pier getting damaged under the events of ground excitation which makes the researchers to find new ways of designing a more ductile, lightweight and cheaper pier along with its foundation. This study presents a pier of multiple steel pipes integrated by shear links. It also includes a comparison of pier performance with and without foundation and hence evaluate which type is better for the proposed structure. It is expected that primary members (columns and piles) should remain safe and damage should concentrate at secondary members (shear links) under the action of seismic excitation. This is what we call damage control design concept.

Keywords: Pier, shear links, damage control design.

Абстракт

Конструкция фундамента опоры моста следующего поколения, основанная на концепции проектирования защиты от повреждений

Опора считается ключевым элементом конструкции моста, поскольку она должна безопасно передавать нагрузку на пролетное строение. Однако всегда существует высокий риск повреждения опор в результате пучения грунтов, что заставляет исследователей искать новые способы проектирования более пластичного, легкого и дешевого фундамента моста. В этом исследовании представлена опора из нескольких стальных труб, соединенных поперечными звеньями. Она также включает в себя сравнение производительности опор с фундаментом и без него и, следовательно, оценку того, какой тип лучше подходит для предлагаемой конструкции. Ожидается, что первичные элементы (колонны и сваи) должны оставаться в безопасности, а повреждения должны концентрироваться на вторичных элементах (поперечных звеньях) под действием сейсмического возбуждения. Это то, что мы называем концепцией дизайна контроля повреждений.

Ключевые слова: опора, срезные звенья, конструкция защиты от повреждений.

Introduction

In bridge structures, column or pier is one of the most important structural members as it supports the whole structure above while standing below it. If pier is damaged, whole bridge structure is under great risk of failure. Therefore, it is necessary to design bridge piers with great care so that it safely transfers the superstructure load to foundation. This requires the conventional design to be followed with “the strong column and weak beam concept”. In the event of strong earthquakes, column has to remain completely safe, courtesy of its large stiffness, however, beam column joints undergo plastic deformations and convert into plastic hinges. Plastic hinges act as energy dampers to dampen the seismic motion. However, these plastic hinges also cause large residual deformations in the event of large earthquakes and requires the restoration. But the problem is restoration time, which is quite large and results into traffic closure and economic turmoil. Similarly, the initial construction costs of these piers with foundations are quite high.

Therefore, a new bridge column formed by integrating multiple steel pipes through shear panels is proposed. In the structure, pier is replaced by four interconnected steel pipes through shear panels and pipes run all the way to the piles without any footing. Here vertical load is carried by the steel pipes and lateral is to be supported by the shear panels/links. Shear panels are made up of a steel type that yield early and possess hysteretic energy dissipation properties. Therefore, during an earthquake, all the seismic action is diverted to the shear panels and they undergo large deformation and damages, preventing the failure of the columns and the whole structure. This is termed as damage control philosophy as allowed to happen only in a certain part which doesn't render damage to the structure overall. Additionally, the restoration time is very low as the shear panels could be replaced easily after the incident. This research study will look into the performance of this bridge structure without foundation through experimental testing and numerical simulations.

Research Objectives

The objectives of this research study would be following:

1. To compare the seismic performance of both (footing type vs footing-less type)

- Axial force acting at pile heads

- Lateral displacement at a pier top and pile heads

- Cross sectional force acting in a bridge column and piles

2. To confirm the yield order of the member for the proposed structure

3. To check the behavior of the proposed structure in liquefiable sand

4. To identify the structural issues of the proposed type

Research Plan

In today's world, it has become a need to connect the various points through overhead bridges due to space limitations on the ground. Bridges carry huge amount of load as they are meant to carry the traffic from one point to another safely and smoothly. They are subjected to static as well as dynamic loads and therefore each structural member needs to be design accordingly. Pier is probably the most important member in the system as it transfers load from the deck to foundation underneath and bears the lateral earthquake loads as well. This makes pier quite bulky heavy and makes the structure expensive overall. In the event of some strong ground motion, the amount of damage to pier could exceed its permissible limits and the whole structure may collapse. However, this is not the case generally, and it undergoes some damages that requires restoration.

The retrofitting and restoration work for the conventional piers is costly as well as time consuming. In this proposal, a relatively new concept of constructing bridge piers is presented. This bridge pier consists of four interconnected steel pipes to carry vertical loads and shear link positioned at various points along the length of pier to carry horizontal loads as shown in the figure (Pict. 1). It is planned to directly connect the steel pipes with piles underneath with no conventional footing. The bridge would be called as footing less having steel pipes interconnect by shear links and jointed with the piles directly. However, a comparison of the footing less vs with footing pier is also planned in this study.

Picture 1. Proposed bridge pier with footing vs without footing (Courtesy of Koichi Isobe (Hokkaido University) et. al [1])

[1] showed a head-to-head comparison of pier made of interconnected steel pipes (footing-less) against steel bridge pier with caisson foundation and pile foundation, and integrated columns pier with footing. And it was shown that pier made of interconnected steel pipes (footing-less) costs 59% lesser and 35% lesser construction time against steel bridge pier with pile foundation. [1] also showed that under the action of same ground motion, the maximum tensile and compressive strain at the base of the columns (footing-less) with underground beam) is 0.73єу and respectively against the similar kind of pier but with the footing and as much as nine piles. [2] showed that it is a reasonable damage control structure as it employs the shear links for strain reduction of columns and causes strain decentralization at the footing point. It is shown that under the action of seismic motion, it behaves in such a way that main members (columns and piles) yield after the shear panels absorb energy and yield. And in particular, the footing-less type integrated columns with an underground beam have higher seismic performance as its main members hold large residual strength even after the yielding of residual deformation. It's very easy to inspect the damages after earthquakes and quick to repair as it requires the replacement of shear panels only.

In this research study, extensive research on this type of pier is planned. It will include the experimental testing as well as the numerical simulation of the problem.

Research Methodology

This research study was carried out in an experimental fashion by my supervisor in collaboration with Hanshin Expressway and Kyoto University. The experimental study included the model development for the proposed bridge pier with and without footing, preparing liquefiable soil and conducting tests under seismic loading. The results of these tests would be used as reference in this study.

This study deals with the numerical modeling of the proposed pier type in DELEAVES soil-water coupling FE analysis code [3]. In order to determine various soil parameters, consolidation test, triaxial test and cyclic triaxial tests etc. are to be performed as well. And then parametric studies would be conducted to simulate the experimental results. Following figure (Pict. 2) shows the type of numerical model to be developed for simulation.

Picture 2. Finite Element Mesh of bridge pier structure Courtesy: Koichi Isobe [1]

Research Outcomes

The outcomes of this research would be the exploration of load transfer mechanism of integrated column piers connected directly to the pile's underneath. It is expected that the results would strengthen the case of proposed pier type as it would be more flexible, reliable and economical structure. Similarly, it is also expected that the behavior of this structures in the problematic soil would prove to be much better than conventional types. Additionally, the yielding order for various structures members would be checked again to show that how this next generation smart bridge structure is based on damage control design concept.

pier steel pipe

References

1. Shinohara M., Kanaji H., Oniki K., Kimura M. (2013). A Proposal of a Bridge Column integrated by Multiple Steel Pipes with Directly-Connected Piles and a Seismic Response Analysis. Journal of Japan Society of Civil Engineers, Ser: C (Geosphere Engineering), 69, 312-325.

2. Isobe K., Sugiyama H., Shinohara M., Kobayashi H., Sawamura Y., Mitsuyoshi Y., Kimura M. (2015). Shaking table test and numerical simulation on seismic performance of a bridge column integrated by multiple steel pipes with directly-connected piles. Japanese Geotechnical Society Special Publication, 1(6), 35-40.

3. Ye B., Ye G., Zhang F., Yashima A. (2007). Experiment and numerical simulation of repeated liquefaction-consolidation of sand. Soils and Foundations, 47(3), 547-558.

Размещено на Allbest.ru