Finite element analysis of the PreWEC self-centering concrete wall system

doi:10.1016/j.engstruct.2016.02.029

Engineering Structures

Volume 115, 15 May 2016, Pages 28-41

https://doi.org/10.1016/j.engstruct.2016.02.029 Get rights and content

Highlights

•
A finite element model was developed for a self-centering precast concrete wall system.
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The model accurately captured the cyclic lateral-load response of a test wall.
•
Energy dissipating connectors can be added to the system without altering the wall axial load.
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Wall axial load ratios should be kept below 10% to avoid significant toe damage.
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Wall-to-floor connection design is critical to the building lateral-load response.

Abstract

A self-centering concrete wall system has been developed that consists of a Precast Wall with End Columns (PreWEC). A finite element model was developed to investigate the cyclic lateral-load response of the PreWEC system that included allowance for uplift at the wall-to-foundation interface, inclusion of the energy dissipating O-connectors, and inelastic behaviour of the confined concrete in the toe of the wall. The model showed good correlation with the results of a large-scale experimental test of the PreWEC system for both the global and local responses, closely matched the experimental lateral force–displacement response, unbonded tendon stress, neutral axis depth, concrete compressive strains, and connector deformation. Additional analyses were conducted to investigate modifications to the PreWEC design. These modified designs highlighted the influence of the inelastic behaviour of the wall toe and showed that in the PreWEC system the axial load on the wall panel is independent of the number of energy dissipating connectors. Lastly, analyses were conducted to investigate wall-to-floor interaction with the PreWEC system. It was shown that a rigid wall-to-floor connection would result in some damage to the floor diaphragms and an overstrength that should be considered when designing the wall for shear. Alternatively, connectors could be used with the PreWEC system to isolate the floor from the uplift of the wall and eliminate damage to the floor diaphragm.

Introduction

Self-centering concrete wall systems that can resist seismic lateral loads without causing significant structural damage have been previously investigated both analytically and experimentally [1], [2], [3], [4], [5], [6]. However, the limited implementation of these wall systems led to the development of a new configuration of self-centering walls that consists of a Precast Wall with End Columns (PreWEC) [7]. As shown in Fig. 1, the PreWEC system utilises a single precast concrete wall panel with two steel or concrete end columns that are each anchored to the foundation using unbonded post-tensioning. The wall and columns are joined horizontally using special connectors positioned along the vertical joints to provide additional energy dissipation. When subjected to a lateral load, the PreWEC system concentrates inelastic deformation at the wall base using a rocking mechanism. The post-tensioning tendons are unbonded to reduce their strain demand and are designed to remain elastic up to the design level drift, providing a restoring force to self-center the structure. Using this arrangement of components, the PreWEC system maximises the lever arm between the post-tensioning tendons and the compression block in the wall toe and can be designed to have a moment capacity equal to that of a comparable monolithic reinforced concrete wall [7].

An experimental test of a 6 m high 50% scale wall specimen was previously conducted to verify the PreWEC concept [7] and a simplified design procedure that was developed by Aaleti and Sritharan [8]. The simplified design method was able to capture the monotonic backbone response of the PreWEC wall, but a more detailed numerical model was required to capture the full cyclic lateral-load behaviour. A non-linear finite element model (FEM) was developed to represent all of the main components of the PreWEC system. The FEM explicitly considered the wall and column uplift and contact length, changes in post-tensioning stresses, connector deformation and hysteresis behaviour, and inelastic strains in the confined concrete compression toe. The developed FEM was used to conduct parametric analyses to better understand the cyclic response of the PreWEC system as well as consider system level effects such as the wall-to-floor interaction that must be accounted for during the seismic design of such buildings.

Section snippets

Development of PreWEC FEM

The FEM developed for the PreWEC system was first validated against the previously tested PreWEC wall [7]. The PreWEC FEM extended on separate models that had been applied to post-tensioned concrete wall panels and the O-shaped energy dissipating connectors [9], [10].

PreWEC cyclic response

The PreWEC FEM was subjected to the full reverse cyclic lateral load history that was applied during the PreWEC test and the calculated response was compared with the measured experimental results.

Modified PreWEC designs

Following the successful validation described above, the PreWEC FEM was used to study the influence of the major design parameters in the wall system. Based on design calculations the connectors accounted for only 35% of the total moment capacity of the PreWEC test wall, but perfect self-centering behaviour was not achieved due to inelastic strains in the wall toe. Although the residual drifts measured during the PreWEC test were still within acceptable design limits, a series of modified

Interaction with floor diaphragms

A critical consideration when examining the seismic response of a building with self-centering walls is how the wall system interacts with the floor diaphragms. The uplift at the base of the wall causes a vertical displacement and rotation at the location of the wall-to-floor connections. Despite also occurring in reinforced concrete wall buildings, wall-to-floor interaction is a particularly important consideration for the post-tensioned wall systems due to the low-damage design philosophy.

Conclusions

A FEM was developed to model the cyclic lateral-load response of the PreWEC self-centering concrete wall system. The FEM replicated each of the components in the PreWEC system and included allowance for uplift at the wall-to-foundation interface, energy dissipating O-connectors, and inelastic behaviour of the confined concrete in the toe of the wall.

Overall, the FEM showed good correlation with the results from the PreWEC experimental test for both global and local responses. The FEM closely

Acknowledgements

Funding for this research was partially provided by NSF grant CMMI 1041650, for which Dr. J. Pauschke served as the Program Director, in addition to Fulbright New Zealand, the New Zealand Ministry of Research, Science and Technology, and the University of Auckland. Opinions, findings, conclusions, and recommendations in this paper are those of the authors, and do not necessarily represent those of the sponsors.

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View full text

Finite element analysis of the PreWEC self-centering concrete wall system

Highlights

Abstract

Introduction

Section snippets

Development of PreWEC FEM

PreWEC cyclic response

Modified PreWEC designs

Interaction with floor diaphragms

Conclusions

Acknowledgements

Eng Struct

Structures

Eng Struct

Preliminary results and conclusions from the PRESSS five-story precast concrete test building

PCI J

Lateral load tests of unbonded post-tensioned precast concrete walls

ACI Spec Pub

Lateral load behavior and seismic design of unbonded post-tensioned precast concrete walls

ACI Struct J

Seismic performance of self-centering structural walls incorporating energy dissipators

J Struct Eng

Hybrid post-tensioned precast concrete walls for use in seismic regions

PCI J

Dynamic testing of precast, post-tensioned rocking wall systems with alternative dissipating solutions

Bull New Zealand Soc Earthq Eng

Precast concrete wall with end columns (PreWEC) for seismic resistant design

Earthq Eng Struct Dynam