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Assessment of RC walls with cut-out openings strengthened by FRP composites using a rigid-plastic approach
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.ORCID iD: 0000-0001-9423-7436
Department of Civil Engineering, Technical University of Denmark, Technical University of Denmark, Division of Structural Engineering.
Technical University of Denmark, Division of Structural Engineering.
Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.ORCID iD: 0000-0002-8682-876X
Number of Authors: 42017 (English)In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 150, p. 585-598Article in journal (Refereed) Published
Abstract [en]

Building refurbishment works frequently require the cutting of new openings in concrete walls. Cutting new openings weakens the overall response of such elements, so they usually require strengthening. However, current design codes offer little guidance on strengthening walls with openings, and less still on the use of non-metallic reinforcements such as FRP (Fibre Reinforced Polymers) to ensure sufficient load bearing capacity. This paper proposes a new procedure based on limit analysis theory for evaluating the ultimate load of walls with cut-out openings that have been strengthened with carbon-FRP (CFRP). First, the approach is verified against transverse (out-of-plane) and axial (in-plane) loading for unstrengthened specimens. These loading types result in different failure mechanisms: transverse loading leads to failure due to yielding/rupture of the steel reinforcement while axial loading leads to failure by concrete crushing. Second, the proposed method is further developed for CFRP-strengthened specimens under axial loading. It accounts for the contribution of CFRP indirectly, by updating the concrete model with an enhanced compressive strength as a result of confining the piers. Predictions made using the new method agree closely with experimental results.

Place, publisher, year, edition, pages
Elsevier, 2017. Vol. 150, p. 585-598
National Category
Infrastructure Engineering
Research subject
Structural Engineering
Identifiers
URN: urn:nbn:se:ltu:diva-9022DOI: 10.1016/j.engstruct.2017.07.069ISI: 000413125800044Scopus ID: 2-s2.0-85026533028Local ID: 794c01ea-1ee7-4cdf-8f59-1d088954f9bfOAI: oai:DiVA.org:ltu-9022DiVA, id: diva2:981960
Note

Validerad; 2017; Nivå 2; 2017-08-15 (andbra)

Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-11-24Bibliographically approved
In thesis
1. CFRP Strengthening of Cut-Out Openings in Concrete Walls – Analysis and Laboratory Tests
Open this publication in new window or tab >>CFRP Strengthening of Cut-Out Openings in Concrete Walls – Analysis and Laboratory Tests
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Redesigning buildings to improve their space efficiency and allow changes in use is often essential during their service lives to comply with shifts in living standards and functional demands.This may require the introduction of new openings in elements such as beams, walls, and slabs,which inevitably reduces their structural performance and hence requires repair or strengthening.However, there are uncertainties regarding both the effects of openings and the best remedial optionsfor them. Traditionally, two methods have been used to strengthen reinforced concrete (RC) walls with openings, these being either to create a frame around the opening using RC/steel membersor to increase the cross-sectional thickness. Currently, intervention in existing buildings must be minimal in order to minimise inconvenience caused by limiting the use of the structure during repairs. One option is to use externally-bonded fibre-reinforced polymers (FRPs).

In this study, the author reports on an experimental investigation of the effectiveness of carbonFRP (CFRP)–based strengthening for restoring the axial capacity of a solid reinforced concretewall after cutting openings. Nine half-scale specimens, designed to represent typical wall panels in residential buildings with and without door-type openings, were tested to failure. The walls were tested in two-way action and subjected to axial loading with low eccentricity (defined as one sixth of the wall’s thickness) along the weak axis to represent imperfections due to thickness variation and misalignment of the panels during the construction process. An extensive instrumentation scheme was used to monitor the specimen’s behaviour during the loading cycles. In addition to classical approaches for measuring strains and displacements, optical 3D measurements were also acquired using the digital image correlation (DIC) technique. These provided better overviews of the failure mechanism by recording the crack pattern development and deformation of the walls throughout the loading history.

Reducing the cross-sectional area by cutting out openings i.e. 25% (hereafter referred to as small opening) and 50% (hereafter referred to as large opening) led to 36% and 50% reductions in peak loads, respectively. In both situations the failure was brittle due to crushing of concrete with spalling and reinforcement buckling. The CFRP strengthening increased the axial capacity of walls with small and large openings by 34 – 50% and 13 – 27%, respectively. This partially restored theircapacities to 85 – 95% and 57 – 63% of their precutting capacity (i.e. solid wall), respectively. A procedure based on a rigid-plastic approach for evaluating the ultimate load of walls with cut-out openings that have been strengthened with FRPs was also proposed in this study. Predictions made using the proposed method agree closely with experimental results.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2017. p. 159
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Building Technologies
Research subject
Structural Engineering
Identifiers
urn:nbn:se:ltu:diva-61515 (URN)978-91-7583-794-9 (ISBN)978-91-7583-795-6 (ISBN)
Public defence
2017-02-23, F1031, Luleå, 10:00 (English)
Opponent
Supervisors
Note

Examining Committee: Professor Karin Lundgren, Division of Structural Engineering, Department of Civil and Environmental Engineering, Chalmers University of Technology, Gothenburg, Sweden

Professor Henrik Stang, Section for Structural Engineering, Department of Civil Engineering, Technical University of Denmark, Lyngby, Denmark

Professor Mats Oldenburg, Division of Mechanics of Solid Materials, Department of Engineering Sciences and Mathematics, Luleå University of Technology, Luleå, Sweden

Available from: 2017-01-20 Created: 2017-01-18 Last updated: 2017-11-24Bibliographically approved

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Popescu, CosminSas, Gabriel

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