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Rain penetration control with architectural precast rainscreen wall
panels
Brown, W. C.
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Ra in pe ne t ra t ion c ont rol w it h a rc hit e c t ura l pre c a st ra insc re e n w a ll
pa ne ls
N R C C - 3 8 5 8 0
B r o w n , W . C .
O c t o b e r 1 9 9 4
A version of this document is published in / Une version de ce document se trouve dans:
CPCI Update, pp. 4, October, 1994
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Canadian Prestressed Concrete Institute
October 1994
CPCI Launches Bridge Software Development
CPCI is proceeding with the development of bridge analysis software. The program will run in Microsoft Windows and be written in accordance with the Canadian Highway Bridge Design Code (CHBDC) and the AASHTO - Load Factor Resistance Design (LFRD) in SI metric units.
The software will be designed to: • Draw the bridge, bridge span and the
beam to be designed graphically on the screen.
• Graphically define all loads (static and moving) and boundary cond-itions for the defined structure. • Graphically define all of the other
parameters such as reinforcement placement and cross sectional properties.
• Graphically display all of the results such as the shear and moment diagrams, stress contours on the planes of the bridges and the resulting design reinforcement • Solve the structure using finite
element analysis or simplified frame elements (user choice).
• When the finite element solution is selected, the program will have auto-mesh generation capability which will reduce the user input to a minimum.
Combinations of prestressed (pre-tensioned or post-(pre-tensioned) and
non-prestressed reinforcement can be specified.
The first version of the program will analyze straight bridges. Girders must be straight and parallel to the centreline of the bridge. The deck must be straight and regnlar in plan with no taper or horizontal curves. Piers and abutments can be skewed at different angles.
The programwill analyze the following types of bridges: Slab Girder Bridges
• single spans
• semi-continuous spans (continuous for superimposed loads ouly) • continuous spans
Spliced Girder Bridges • single spans
• continuous spans
Cast-In-Place Slab Element Bridges • single spans
• continuous spans
Cast-In-Place Box Girder Element Bridges
• single spans • continuous spans
The program will analyze ouly the bridge superstructure. The sub-structure will be modelled as spring supports to give users an indirect method of including substructure effects.
The program will check the ade-quacy of any design options provided
by the user (size, shape and spacing of concrete elements). Some assistance will be provided to the user in determining the location and amount of prestressed .and non-prestressed reinforcement at various construction stages.
The software will be written in discrete modules. This will facilitate adding additional features during future upgrades to the program.
CPCI has assembled a review committee ofvolunteers from industry, consulting firms, universities and provincial bridge engineers to advise and test the software during its development Please contact CPCI to obtain more information about the software or to participate and assist with the project.
Winsoft Software Inc. will do the programming.Mr. Kris Bassi and Dr. Ghani Razaqpur will act as consult-ants to CPCI. CPCI gratefully acknowledges NRC for providing financial assistance for the project under its!RAPprogram.
Progress
Milestone I has been completed. Work is proceeding on Milestones 2 and 3 (see Miles/ones - page 2). Completion of Milestone 4 is scheduled for the end of 1994. At that time, a working version of the solver can be distributed to the review committee for beta testing.
The working program is scheduled to be available for general sale and use by the end of 1995.
,.".
The
Network of
Centres of Excellence
on High-Performance Concrete
Concrete Canada
Carolyn M. Hansson Queen's University Carmel Jolicoeur Universite de Sherbrooke Jim G. MacGregor University of Alberta Denis Mitchell McGill University Rusty Morgan HBT Agra Ltd. Michel Pigeon Universite Laval Phil T. Seabrook Levelton Associatesand is chairman of the demonstration projects which Concrete Canada will carry out.
Concrete Canada is keen to interact with the concrete industry and will continue to liaise with CPCI.
The fourteen principal investi-gators involved with ihe research are:
Pierre-Claude Aitcin Universite de Sherbrooke Gerard Ballivy
Universite de Sherbrooke Jim J. Beaudoin
Institute for Research in Construction Ted W. Bremner
University of New Brunswick Michael P. Collins
University of Toronto Walter H. Dilger University of Calgary
In addition, Yves Delagrave is the Network manager as well as the implementation manager for the province of Quebec.
John A. Bickley is the implement-ation manager for the rest of Canada Denis Mitchell
Phase I of the High-Performance Concrete Network finished in March I994. The Network prepared a new application for funding in Phase II and entered a competition against the other 14 networks. OnMarch 28, 1994, the Federal Government announced the names of tIie ten Networks that will be funded in Phase II.
Fortunately the High-Performance Concrete Network was successful in its request for fimding in Phase II. The
new Network will be called Concrete L --l
Canada and will focus on using high-performance concrete to improve Canada's infrastructure and inter-national competitiveness.
Concrete Canada was awarded $5.5 niillion over a four year period.
Bridge Software Project Milestones
MILESTONE 1Code Formulae and Design Flow Chart
Study the design codes and sununarize all of the formulae used in each code. Provide the mathematical formulae for the generation of loads and forces and the analysis of the concrete sections as outlined in current industry practice and in conformance with .the CHBDC and the AASHTO design codes. Develop a set of diagrams displaying preliminary dialogue boxes and flow charts of the program operation.
MILESTONE 2
Numerical Investigation and Planning
Develop a set of at least 10 design problem solutions which will indicate the range of bridge types and configurations the program will be capable of solving. In cases where hand solutions are not possible, use assumed values to allow the problem
tobe carried out.
MILESTONE 3 The Input Module
Develop the module which will allow the definition and input of all of the data required for any design solution. Have all dialogue boxes for data input ready and operational. MILESTONE 4
The Solve Module
Program the finite element formulae as applicable to the precast prestressed or post-tensioned concrete elements. The program at this stage will be capable of inputting data and solving for the structural response under applied loads. Generate design results for beta testing by the review committee.
MILESTONES
The Prestressed Element Design Module
Develop the continuous span pretensioned design module. Generate design results for beta testing by the review committee.
MILESTONE 6
The Post-Tensioned Element Design Module
Develop the continuous span post-tensioned design module. Generate design results for beta testing by the review committee.
MILESTONE 7 The Post Processor
Develop the bridge analysis results module complete with plots, graphs and tables.
MILESTONE 8 Manual Writing and Final Beta Testing
Complete the User's Manual. Complete final testing of the software by the review cotnmittee. Develop and print marketing brochures to introduce and explain the features of the software.
1994 CSA A23.3
New Changes Affecting the
Precast Prestressed Concrete Industry
Book Review
Precast
Building
Structures
Planning and Oe.lgnThe book covers the same basic ground as many CPCI and PCI publications in an interesting .and inforritative way; the difference being the European examples and approach to precasting. There are some good applications and framing ideas that should be of interest to Canadian design engineers and precasters.
This new, 140 page, hard cover, handbook from the FIP CommissiQn on Prefabrication is very well illust-rated by numerous colonr and black and white photographs, together with plan and isometric drawings and plenty of constructiQn details.
the FIP precast handbook merits close scrutiny and shQuld be part Qf everyone's reference library.
Available from:
Federation Internationale de la Precontrai"t (FIP)
Administrative Office 11 Upper Belgrave Street London SWIX 8BH Tel: 011 44 71 235 4535 Fax: 011 44 71 235 4294
The book contains chapters covering the suitability of precast concrete, preliminary design consid-erations, examples of precast buildings, general design principles, frame and skeletal structures, precast floors, bearing walls and architectural concrete facades.
These requirements consist of: • miuimum horizontal and vertical tie forces between floor and roof diaphragms and wall panels,
• minimum capacities for precast columns,
• miuimum tension tie forces around the perimeter ofeach floor and roof. 3. High Strength Concrete
There are a number of changes throughout the code that applytohigh strength concrete.
These include:
• mlOlmum flexural and shear reinforcement equations that are a function of concrete strength,
• more closely spaced ties will be required in coluDlDs ifthe concrete compressive strength exceeds 50 MPa, • new stress block factors for determiuing the factored flexural resistances of members.
CPCI Publications
4. Clause 18 - Prestressed Concrete Clanse 18.7 has new expressions for the stress in prestressed tendons at factored resistance but also permits the determination of the factored resist-ancebasedon strain compatibility.
Resowmended Practice MetricDesignManual Precast and Prestressed Concrete Second Edition (1987)
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Prestressed Concrete Basics
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The architectural precast projects illustrated reflect a number of styles and designs favoured by EurQpean .... ... architects which may well- provide inspiration to Canadian designers looking for something a little different. Denis Mitchell
The CSA Standard A23.3, "Design of Concrete Structures" has been finalized. The new standard will be issued in late 1994.
There are several issues which will affect the precast prestressed concrete industry.
1. Clause 16 - Precast Concrete Clause 16.1.3 gives an increase in the concrete material resistance factor, from 0.60 to 0.65 for "elements produced in manufacturing plants certified in accordance with Clause 16.2", (i.e., manufactured and erected in accordance with the requirements of CSA A23.4, "Precast Concrete Materials and Construction").
This cbange will give about an 8% increase in shear capacities for members without stirrups and will give a smaIl increase in the factored flexural resistances of precast members.
2. Clause 16 - Precast Concrete Clause 16.5 gives requirements for structural integrity.
1994 Martin P. Korn Award
PCI has selected Robert E. Loov and AnilK. Patnaik as the recipients of the 1994 Martin P. Korn Award for their paper "Horizontal Shear Strength of Composite Concrete Beams With a Rough Interface". This annual award recognizes the paper published in thePCI Journal worthy of special CPCI Software commendation for its merit as a con·
tribution in design and research to the CONCISE Beam version 2.0 CAD Precalt PrestreNed Beams advancement of precast prestressed MI<...ftWlndo",3.1Softwa...
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em 0 gary. quattons are Callrora ...Demo. Price _30 British pounds (includes proposed for evaluating the horizontal NowLowPrl"l shipping& bandll·ng).
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Architectural Precast Rainscreen Wall Panels Control Rain Penetration
wUUamC. BrownArchitectural precast wall panels can
provide more than an attractive,
economical, long-lasting exterior cladd-ing for buildcladd-ings. With appropriate design, precast panels can provide a high performance wall system which will control rain penetration.
Rain penetration control strategies for precast walls range from face seal designs to pressure equalized rainscreen (PER) designs. The face seal approach relies heavily on the use of sealants, which need regular maintenance to achieve the required service life. The performance benefits gained by the use of a PER precast wall system should more than offset any extra capital cost.
Rainscreen walls consist of three
elements - an exterior cladding or
rain-screen, an air barrier system containedin
the interior assembly and a vented air space separating the two (which should direct any water entering the cladding back to the exterior). The rain penetration forces controlled by a PER wall system include the kinetic energy of rain drops, surface tension and capillarity, gravity and air pressure differences. The design of a PER wall must address both static and dynamic (wind) pressure differences
and such parameters as the size and
location of the venting, volume and flexibility of the air space, location of compartment seals and loads on the barrier system and on the rainscreen.
To determine precise design guidelines for PER walls, NRC and CMHC are jointly sponsoring an experimental project which includes testing several COmmon wall systems. Two precast concrete sandwich panel test specimens measuring 2.43 m high by 1.19 m wide were constructed by Central Precast Limited, Ottawa, for the project.
Both panels had a 100 mm thick precast concrete inner leaf which functions as the air barrier system, 52 mm of extruded polystyrene insulation,
an air space, and a 65 mm precast
concrete outer leaf which functions as the rainscreen. The air space for, one speoimen had an open 13 mm wide cavity. The air space for the other specimen was formed using a 12 mm deep stiff dimpled plastic sheet material called Miradrain. Both cavities extended over the full height and width of the specimen. The inner and outer leafs were connected by two stainless steel trusses. The specimens had a38mm high bottom vent, the full width of the specimens.
The rain penetration control perform-ance of the test specimens was evaluated in NRC's Dynamic Wall Test Facility
(DWTF) which enables NRC scientists to simulate dynamic wind-driven rain
conditions on the test specimens. The
DWTFis capable of producing pressure excitation at frequencies up to5Hzand static pressures up to 10 kPa. Water can
besprayed on the specimens at rates up to 10 Ilmin1m'.
Experimental Re.u1ts
The first test determined the effeet of
various parameters on the pressure
equalization response of the specimens. The experiments found no significant difference in the two specimens, with the air space formed by the Miradrain exhibitingthesame response as the open cavity. A minimum of three 13 mm diameter vent holes were found to provide adequate pressure equalization in the test specimens with a tight air barrier system. The response of the specimens deteriorated as leakage in the air barrier
system was increased. Five 13 mm
diameter vent holes were required to obtain adequate response with three 7 mm diameter leakage holes.
A second experiment determined the rain penetration control performance of the specimens. A deliberate defect was. formed by a 64 mm deep by 5 mm wide saw cut in the rainscreen. The amount of water passing the rainscreen withastatic pressure difference was determined. Approximately 0.2 IImin passed the rainscreon through the 'defect' when there was no pressure difference 'across it (gravity driven rain). This rose to 0.6
lImin at static pres'sure differences greater than 100 Pa.
The amount of water passing the rainscreen through the 'defect' when a dynamic pressure difference was applied was determined. With no venting and a leaky air barrier system (three 7 mm diameter holes), greater than0.5 IImin passed the rainscreen. Less than 0.4
llmin was measured when the air barrier system was sealed. This was further reduced to about 0.2 I/min when five vent holes were opened. These results dramatically indicate the combined benefits of proper venting and an effective air barrier system in achieving the successful control of rain penetration. Conclusion.
These. experiments demonstrate that architectural precast rainscreen wall panels canbe manufactured tc control rain penetration using the pressure equalized rainscreon design principle.An
effective air barrier system is an inherent feature of such panels. A sheet material like Miradrain can provided a simple, but
･ｦｦ･｣ｴｩｾ･Ｎ means of providing an air space.
Adequate venting canbeprovided with a 12 mm high opening located at the bottom of the air space which extends for the width of the panel. This design detail will minimize the static and dynamic pressure difference induced by wind across the rainscreen.
Canadian Prestressed Concrete Institute
196 Bronson Avenue, Ottawa, Ontario, Canada K1R 6H4
TEL: (613) 232-2619 FAX: (613) 567-3064
For further information - contact: John R. Fowler P. Eng., President The Canadian Prestressed Concrete Institute is a non-profit institute.
CPCI's purpose is to advance the useofstructural precast concrete, architectural precast concrete and post-tensioned concrete construction in Canada.
