A STUDY ON LOAD BEARING CAPACITY OF SANDWICH WALL PANELS Rupasinghe Arachchige Don Lalindra Jayamevan Rupasinghe (09/8927) Degree of Master of Engineering in Structural Engineering Designs Department of Civil Engineering University of Moratuwa Sri Lanka January 2013
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A STUDY ON LOAD BEARING CAPACITY OF
SANDWICH WALL PANELS
Rupasinghe Arachchige Don Lalindra Jayamevan Rupasinghe
(09/8927)
Degree of Master of Engineering in Structural Engineering Designs
Department of Civil Engineering
University of Moratuwa
Sri Lanka
January 2013
A STUDY ON LOAD BEARING CAPACITY OF
SANDWICH WALL PANELS
Rupasinghe Arachchige Don Lalindra Jayamevan Rupasinghe
(09/8927)
Dissertation submitted in partial fulfillment of the requirements for
the degree Master of Engineering in Structural Engineering
Department of Civil Engineering
University of Moratuwa
Sri Lanka
January 2013
i
Declaration
I declare that this is my own work and this dissertation does not incorporate without
acknowledgement any material previously submitted for a Degree or Diploma in any
other University or institute of higher learning and to the best of my knowledge and
belief it does not contain any material previously published or written by another
person except where the acknowledgement is made in the text.
Also, I hereby grant to University of Moratuwa the non-exclusive right to reproduce
and distribute my dissertation, in whole or in part in print, electronic or other
medium. I retain the right to use this content in whole or part in future works (such
as article or books).
Signature: ………………………………… Date:……………………….
R.A.D.L.J. Rupasinghe
(09 / 8927)
The above candidate has carried out research for the Masters Dissertation under my
supervision.
Signature: ………………………………… Date:……………………….
Research Supervisor
Dr.K.Baskaran
Senior Lecturer
ii
Abstract
Sandwich wall panel technology is a new system introduced to Sri Lanka. Thermal insulation, sound insulation, light weight and reduction in natural resources like sand have lead to its popularity in Sri Lanka. The system is faster in construction than conventional wall systems. The sandwich wall panel system is used in Sri Lanka as partitioned walls in construction industry today. Load from above floors are taken by separate column and beam system. If accurate load bearing estimate is available, it can minimize or omit use of other load bearing systems. The scope of this research was to recognize suitability of available codes and to identify the reduction in load bearing capacity due to a window opening in a sandwich wall panel. In this dissertation, method of production of locally available sandwich wall panels and load bearing capacity according to available literature are presented. Three 1200mm width, 100mm thick and 2400mm high sandwich wall panels were cast. Out of these three, two panels had openings to represent windows. The panels were tested in axial compression while monitoring transverse deflection at mid height of the panel. All three panels’ ultimate load bearing capacity was nearly equal. Only one panel had higher degree of lateral movement while loading. All panels have shown local crushing failure near top and bottom loading points. Three sandwich panel blocks of 600mm length, 100mm thick and 300mm height were tested in a Universal testing machine to get ultimate load bearing capacity. The blocks’ ultimate load bearing capacities are also nearly equall to that of 2400mm height panels. Six numbers of 150mm mortar cubes were also tested in Universal testing machine to find ultimate compressive strength. Samples of diagonal shear connecters (Gauge 9 GI wire) were cut out from specimen and tested for compression capacity in Universal timber testing machine. The samples failed in buckling. 100mm high samples had about 0.7kN compression capacity. It was concluded that 600mm width and 900mm high opening in the given orientation did not affect load bearing capacity of panel. Key words: Sandwich wall panel, Load bearing capacity, openings, wythe, insulation layer.
iii
Acknowledgement
I wish to express my sincere gratitude to my research supervisor Dr.K.Baskaran,
Senior Lecturer, Department of Civil Engineering, University of Moratuwa, Sri
Lanka for his guidance, suggestions and continuous support throughout my research
work.
I also extend my sincere gratitude to the Head of Department of Civil Engineering,
University of Moratuwa, Sri Lanka for allowing me to use the laboratory facilities
and the resources available at the university, for successful completion of my
research project.
I wish to thank the Micro Construction (Pvt) Ltd for providing sandwich panels and
other test samples for the research. Their kind assistance and knowledge helped me
for the success of my research.
I would like to take this opportunity to convey my sincere gratitude to
Mr.H.N.Fernando (Lab Assistant-Structural Testing Laboratory) for the assistance
extended to me in numerous ways throughout this period.
I also extend my appreciation to my family for the valued cooperation and
encouragement received to make my M. Eng. programme a success.
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Table of Contents
Abstract ii
Acknowledgement iii
Table of content iv
List of Figures vii
List of Tables ix
List of Abbreviations x
1. Introduction 01
1.1 General Introduction 01
1.2 Research Objectives 03
1.3 Research Scope 03
1.4 Outline of the Report 03
2. Literature Review 04
2.1 General Introduction 04
2.2 Materials use for sandwich wall panels 05
2.2.1 Wythes 05
2.2.2 Shear Connectors 05
2.2.3 Insulation 07
2.2.4 Steel reinforcements for wythes 09
2.3 Precast panel sizes 09
2.4 Bowing in sandwich wall panels 10
2.5 Thermal performance 10
2.6 Composite and non-composite behaviour of sandwich wall panel 11
2.7 Axial load bearing capacity 13
2.8 Flexural loading capacity of SWP 24
2.9 Summary 28
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3. Experimental Study 30
3.1 General Introduction 30
3.2 Equipments used to produce SWP 31
3.2.1 Cement mortar sprayer 31
3.2.2 Pair of pliers 33
3.2.3 Pneumatic “c” ring gun 33
3.2.4 Air compressor 34
3.3. Panel casting 35
3.4 150mm Test cube casting 38
3.5 Testing panels under axial compression load 39
3.6 Testing small SWP blocks for compression 42
3.7 Testing mortar test cubes for compression 43
3.8 Testing gauge 9 GI wire diagonal members in compression 43
4. Analysis and Discussion of Results 44
4.1 General Introduction 44
4.2 Experimental results 44
4.2.1 Panel A 44
4.2.2 Panel B 46
4.2.3 Panel C 47
4.2.4 600mm x 100mm x 300mm Blocks in axial compression 49
4.2.5 150mm Mortar cubes in compression 50
4.2.6 Gauge 9 GI wires in compression 50
4.3 Summary of test results 50
4.4 Estimation of axial load capacity according to literature 51
4.4.1 BOCA (1999) 51
4.4.2 ICBO (1999) 52
vi
4.5 Discussion 53
4.5.1 Comparison of Panel A with BOCA (1999) 53
4.5.2 Comparison between Panel A and ICBO (1999) 53
4.5.3 Load bearing reduction due to opening 53
4.5.4 Compression capacity of SWP blocks 54
4.5.5 Comparison of SWP blocks and panels with BS 5628-1 54
4.5.6 Finite element modelling 56
5. Conclusions and Recommendations 57
5.1 General Introduction 57
5.2 Conclusions 57
5.3 Recommendations for Future Works 57
References 59
vii
List of Figures
Figure 1.1 Basic elements of a sandwich wall panel 01
Figure 2.1 Examples for shear connectors 06
Figure 2.2 Non composite and fully composite panels’ theoretical behaviour 11
Figure 2.3 Test set-up and test frame of Benayoune et al. (2005a) 16
Figure 2.4 Top end condition and loading arrangement of Benayoune et al. (2005b) 18
Figure 2.5 The Artzer panel specified by BOCA International Evaluation (1999) 20
Figure 2.6 SWP specified by ICBO (1999) 21
Figure 2.7 Standard KIO panel section 22
Figure 2.8 50mm insulated Micro Construction SWP 23
Figure 2.9 Loading system of first two panels of Benayoune et al. (2006) 24
Figure 3.1 Dimensions of test panels with opening 31
Figure 3.2 Mortar sprayer 32
Figure 3.3 Four nozzles at bottom 32
Figure 3.4 Pair of pliers 33
Figure 3.5 “C” ring cartridge 33
Figure 3.6 Pneumatic C ring gun 34
Figure 3.7 Air compressor 34
Figure 3.8 Marking the opening 35
Figure 3.9 Cutting EPS layer by hacksaw 35
Figure 3.10 Reinforcements tying using C ring gun 36
Figure 3.11 First plaster layer levelling 37
Figure 3.12 Plastering third mortar layer of the wall 37
Figure 3.13 Test cubes casting 38
Figure 3.14 Test setup 39
Figure 3.15 Test setup of panels with opening 40
Figure 3.16 Two dial gauges 41
viii
Figure 3.17 600mm x 100mm x 300mm blocks testing 42
Figure 4.1 Panel A 44
Figure 4.2 Axial load vs. central lateral deflection for Panel A 45
Figure 4.3 Panel B 46
Figure 4.4 Axial load vs. lateral deflection for Panel B 47
Figure 4.5 Panel C 48
Figure 4.6 Axial load vs. lateral deflection for Panel C 49
Figure 4.7 Eccentric load vs. lateral deflection for PA1 at mid-height of the panel 53
Figure 4.8 Axial load vs. lateral deflection for PA1 at mid-height of the panel 54
ix
List of Tables
Table 2.1 Physical properties of insulation material (PCI committee,1997) 08
Table 2.2 Allowable axial load taken from BOCA (1999) report 20
Table 2.3 Allowable axial load taken from ICBO (1999) report 22
Table 2.4 Allowable transverse loads as per BOCA (1999) 26
Table 2.5 Transverse load vs. span for SWP taken from ICBO (1999) 27
Table 4.1 Compression capacity of SWP blocks 49
Table 4.2 Compressive strength of mortar cubes 50
Table 4.3 Summary of results 50
x
List of Abbreviations
SWP : Sandwich Wall Panel
EPS : Expanded Polystyrene Foam
XPS : Extruded Polystyrene Foam
BS : British Standard
GI : Galvanized Iron
PCI : Precast/ Prestressed concrete Institute
BOCA : Building Officials and Code Administrators
ICBO : International Conference of Building Officials
FEM : Finite Element Model
OPC : Ordinary Portland cement
W/C : Water to Cement Ratio
FRP : Fibre reinforced plastic
BRC : Trade name of a wire mesh manufacturer
1
Chapter 1
Introduction
1.1 General Introduction
Sandwich wall panels (SWP) are a building material. They consist of an insulating
layer of rigid polymer foam between two layers of structural board. The board can
be sheet metal, plywood, cement mortar or concrete. The foam can be either
expanded polystyrene foam (EPS), extruded polystyrene foam (XPS) or
polyurethane foam. Metal or FRP connectors are used between two cement mortar
layers or two concrete layers through insulation.
Fig. 1.1 Basic elements of a Sandwich wall panel
Sandwich wall panels share the same structural properties as an I- column or beam,
while structural boards act as the flanges and either rigid insulation or connectors
exhibits the same property as web. SWPs combine several components of
conventional buildings such as load bearer, safety barrier, vapour barrier, air barrier,
noise barrier and heat insulator. Although SWPs are mainly used as exterior walls,
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they can be used for many applications, such as internal walls, roof and floor slabs.
Because of the superior heat insulation property cold countries like Norway use
SWPs as exterior walls with minimum insulation thickness of 200mm, which is
recently regulated by building authorities. Use of SWPs minimize energy
consumption (heating) of the building in long run and maintain in and out
temperature difference of 500C.
According to PCI committee report on “State of the art of precast / prestressed
sandwich wall panels” first use of SWP with foam insulation is unknown but has
evidence of 40 years old structures in United States.
A panel having two inner and outer Zink Aluminium metal sheets filled in between
by polyurethane foam is widely used to construct telecommunication tower base
stations. Light weight, heat insulation, security and quick assemble properties give
much popularity in this use. Generally, concrete and mortar layered SWPs are used
for permanent housing and building constructions. There are two major methods of
constructing concrete SWP. One is precasting on a vibrating table and the other is
in-situ application by shot-crete. Mortar is generally applied on EPS board in-situ by
mortar spraying machine or manual application by trowel.
In contrast with using SWP system in low temperature situation, it can be used in
temperate countries like Sri Lanka to reduce heat transfer and to construct energy
efficient buildings. The system can save air conditioning cost in long run. In Sri
Lanka SWP system had been experimented for housing by several agencies. KIO
Ltd had constructed a model house in Colombo using their SWPs. Micro
constructions Ltd is vastly using commercial SWP system to their projects. Almost
all applications in Sri Lanka are non-load bearing partition type constructions. Load
from upper floors are taken by either concrete or steel column-beam system. There
are very less amount of research and testing had been done for SWPs in Sri Lanka.
Therefore, current research aims to cover some voids in this area.
3
1.2 Research Objectives
First objective is to find suitability of using BS 5628 Masonry code and other codes.
For this, test results of SWPs will be compared to cellular or hollow block masonry
figures in BS 5628. Second objective is to estimate reduction in load bearing
capacity due to window opening.
1.3 Research Scope
The scope of the research includes
Cast actual size wall panels.
Testing panels with axial compression load.
Cast standard test cubes of same mortar mix.
Testing cubes for compression.
Cast 600mm x 300mm x 100mm of standard thickness small blocks.
Test them to find compression capacity.
Comparison of results of blocks and panels with BS 5628.
Comparison of results with available literature.
1.4 Outline of the research report
Chapter 2 presents a review of the literature related to Sandwich Wall Panels,
existing specifications and guidelines for SWPs, transverse flexural capacity, degree
of composite action between structural layers, axial compression capacity with and
without eccentricity and study on different connectors and their quantity. The study
of global research conducted in this area helped in the identification of the gap in
literature and research areas.
Chapter 3 describes the casting and experimental procedures for the present study.
Chapter 4 discusses the experimental results of the research for achieving the
research objectives and scopes.
Chapter 5 summarizes the research study. It presents a summary of findings and
some recommendations for future work.
4
Chapter 2
Literature review
2.1 General Introduction
Precast/Prestressed Concrete Institute [PCI] committee (1997) on precast sandwich
wall panels with chairing Kim E. Seeber had presented an extensive report on
precast sandwich wall panels in 1997, March as “State-of-the-Art of
Precast/Prestressed Sandwich Wall panels”. According to the introduction, “Precast /
Prestressed sandwich wall panels are composed of two concrete wythes (layers)
separated by a layer of insulation such as a flat slab, hollow-core section, double tee,
or any architectural concrete section produced for a single project. In place,
sandwich wall panels provide the dual function of transferring load and insulating
the structure. They may be used solely for cladding; they may act as beams, bearing
walls, or shear walls”.
Precast sandwich wall panels can be used either for exterior or interior walls. This
interior use governs when one area of a building keep higher or lower temperature
than other. A refrigerator or air conditioned room can be considered as an example.
Precast sandwich wall panels can be cast in precast factory and transported to site.
They are erected either in vertically, spanning in between foundation and slabs or
horizontally, spanning between columns. Here, column-beam frame can be steel or
concrete. In the case of load bearing walls, vertically spanned walls support slab
diaphragm without column-beam frame.
SWP has been popular among architects and engineers because of energy
performance. Contractors like SWPs’ nature of quick dried sites which benefits
other trades to work in a clean and comfortable environment.
5
2.2 Materials use for sandwich wall panels
2.2.1 Wythes
Reinforced two structural wythes are composed either with concrete or mortar. PCI
committee (1997) describes minimum layer thickness of 2 Inches (51mm) of
concrete. This layer thickness may be increased due to imposed loading, panel type
and final use. For example, the required fire resistive rating may be the determinant
for the thickness and cover. For same load and span condition a non-composite
panel requires higher thickness than a composite panel. Composite and non-
composite behaviour will be discussed later in the literature review under section
2.6. Exterior surface of panel may get architectural features like form liners, reveal
strips or embedded natural stones. Such a case, to comply with relevant code and
cover requirements layer thickness should be increased. For example, in case of
natural stone finished exterior surface allows air and moisture movement towards
inner surface due to voids between stones. To increase durability wythe thickness
should be increased.
International Conference of Building Officials [ICBO] Evaluation Service, Inc.
(1999) recommends 1 Inch (25mm) minimum layer thickness with Portland cement
mortar plaster for panels addressed there. It also specifies minimum 28 day
compressive strength of 13.8 MPa. According to Building Officials and Code
Administrators [BOCA] international Evaluation Services (1999) nominal thickness
still reduces to 7/8 Inches (22mm) and compressive strength of plaster further
reduces to 10.35MPa.
2.2.2 Shear connectors
Shear connectors are used to tie the two wythes together and to keep the panel intact
during handling and service conditions. These connectors penetrate through weak
insulation layer and bond to each wythe. These connectors come in many different
sizes, shapes and materials. Some of the types and shapes are C-tie, Z-tie, M-tie,
cylindrical metal sleeve anchors, hairpin, circular expanded metal, welded wire
truss, plastic or fiber-composite pins and area of solid concrete (web). All steel
6
connectors should be either Galvanized or stainless steel for durability issues.
Examples for some connectors are shown in figure 2:1, which are illustrated from
PCI committee (1997). Main function of connector is to keep whole panel as one
unit. For example if panel is cast on a vibrating table then it should be able to turn to
vertical position without relative movements between wythes. In case of composite
panel those connectors should be able to transfer shear force between wythes, when
panel is subjected to a transverse flexural or axial loading. Two wythes get tensile
and compressive force while connectors between wythes should bear the shear force
as in a steel I section. In non-composite sandwich panels those connectors are named
as non shear connectors. Examples for non shear connectors are plastic pins, metal
C-ties and continuous welded ladders. Limited number of these connectors
minimises thermal bridging between two wythes. (Thermal bridging is explained
under section 2.5 thermal performance) Main function of this type of connection is
to transfer tensile force between wythes.
Fig 2:1 Examples for shear connectors
Source: PCI committee (1997)
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2.2.3 Insulation
Insulation is the most vulnerable part of SWP when considering durability and
strength aspects. Positioning this weak insulation layer in between two durable and
hard concrete wythes provides the best structural insulation system. Therefore, this
insulating technique provides low maintenance, durable, fire resistant and highest R-
value (Thermal resistance) per unit cost.
Although there are many insulation types on the market today, insulated concrete
sandwich walls utilize a cellular (rigid) insulation because it provides those material
properties that are most compatible with concrete. These compatible material
properties include moisture absorption, dimensional stability, coefficient of thermal
expansion, compressive and flexural strengths. Selection of the type of insulation to
enhance energy performance is as important as the reinforcement needed to enhance
structural performance. Insulation selection can affect the longevity of panel’s
intended effectiveness depending on site location, climate variables and operating
conditions.
Thermoplastic and thermosetting are the two primary forms of cellular insulation
used in the manufacture of sandwich panels. The thermoplastic insulations are better
known as moulded expanded Polystyrene (bead board) and extruded expanded
Polystyrene (extruded board). Thermosetting insulations consist of Polyurethane,
Polyisocyanurate and Phenolic. Physical properties are listed in Table 2.1 which is
published on PCI Committee (1997).
8
Table 2.1 Physical properties of insulation material Physical Polystyrene Polyisocyanurate
Phenolic
Cellular
Property Expanded Extruded Unfaced faced glass Density 11.2-