design and protection in case of fire (sikawrap and sika carbodur)

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TECHNICAL ARTICLEDesign and protection in case of fire

SikaWrap® – Sika® CarboDur®AUGUST 2014 / V1.0 / SIKA SERVICES AG / DAVID VAZQUEZ

FOR INTERNAL DIFUSSION



Technical article

Design and protection in case of fireSika Services AG

SikaWrap® and Sika® CarboDur® For Internal Difussion

August 2014, v1.0

2/12

TABLE OF CONTENTS

1 SCOPE 3

2 INTRODUCTION 3

3 LOADS AND STRENGTHS UNDER A FIRE SITUATION 3

4 PROTECTION OF THE CFRP IN CASE OF FIRE 5

5 FIRE RESISTANCE 5

6 REACTION TO FIRE 7

7 FREQUENTLY ASKED QUESTIONS 7

8 REMARKS 11

9 LEGAL NOTE 12

10 KEY WORDS 12



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1 SCOPE

The design of CFRP for structural strengthening under a fire situation has always been a matter of doubt by our

staff and customers.

However, in most cases, the protection of the carbon fiber laminates may be useless, since no additional safety

measure is required. This assumption includes most of the standard situations. However, and despite being well

covered by the various local and international guides, this topic is a frequent source of problems and

discrepancies.

2 INTRODUCTION

The design of a structure is focused in ensuring the necessary strength under the expected loads. For safety

reasons, the different codes take into account additional safety coefficients, so that the final calculation utilizes

load magnitudes higher than the actual ones, and material´s strengths lower than the real. This way, extraordinary

situations that may exceed the expected, common conditions are equally taken into account.

Situation Eurocode 2 (simplification) ACI 318 (simplification)

Design loads The expected loads are magnified

by means of safety factors:

x 1.5 for variable loads.

x 1.35 for permanent

loads.

The expected loads are magnified

by means of safety factors:

x 1.6 for live loads.

x 1.2 for dead loads.

Design Strengths The material´s strengths are

reduced by means of safety factors:

/ 1.5 for concrete.

/ 1.15 for steel.

The nominal strength of the

member is reduced according to

defined parameters according to

the kind of element and the

expected ultimate strains

(x 0.65 – x 0.9)

As a consequence of this, the structures must be designed so that they necessarily have a resistance substantially

greater than requested to support the anticipated loads. However, under certain circumstances, these conditions

cannot be met either as a consequence of a current resistance lower than the expected, or by the existence of

loads higher than those initially estimated.

Under those circumstances, an appropriate strengthening method must be displayed, so that the structural safety

margin required the local legislation is ensured.

3 LOADS AND STRENGTHS UNDER A FIRE SITUATION

Those systems using CFRP reinforcement methods are widely used today as one of the preferred alternatives by

engineers and contractors, since they involve extremely fast and effective solutions in most of the cases.

However, these systems essentially support those loads that are transferred to them via adhesives used for

placement. Therefore, in those situations where the rapid heating of the bonding agent can be expected, the

integrity of the CFRP solution is constrained to those temperatures below the softening point of the adhesive.

Hence, under a fire situation, the mechanical capacity of the un-protected CFRP laminate will be lost within the

first minutes, so the existing loads must be supported by the original, un-strengthened RC structure. Apparently,

this situation seems to compromise the integrity of the structural element. But, in most cases, this is not the case.

The different existing guidelines take into account this verification in the calculation process. However, the

expected loads in case of fire are notably reduced, as a substantial part of the live loads (variable loads) will not be

expected in case of fire. This fact is clearly defined by the local codes in each territory.



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Similarly, the real strengths of the materials are considered, instead of the design (reduced) ones.

FIRE SITUATION Eurocode 2 (simplification) ACI 318 (simplification)

Design loads

Service, un-factored loads

(e.g. quasi-permanent

combination of loads,

option 1)

Reduced percentage of the

design loads (e.g. 70%,

option 2)

Service, un-factored loads

Design Strengths Real (characteristic) strengths for

concrete and steel.

Nominal strength of the member

These two changes involve that, in a fire situation, the structure will provide a greater resistance against the

expected loads, which are equally reduced. Therefore, in most situations, the original structure without CFRP

reinforcement can withstand loads without any additional strengthening, so that the loss of CFRP has no

consequence.

Problem Solution Fire Situation

The design loads exceed the design strength of

the memberThe contribution of the CFRP increases the

strength of the member. The design loads can

be supported by the strengthened member

Un-protected CFRP is lost. Only part of the

design loads are taken into account for the

calculation, and the existing RC member

exhibits a greater strength due to the absence

of safety factors (according to the local

regulations).

This verification must be done as part of the calculation process. The new Sika® Carbodur® Calculation Software

includes an automatic tool for it:



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4 PROTECTION OF THE CFRP IN CASE OF FIRE

Uncommonly, the mechanical contribution of the CFRP strengthening is absolutely necessary in case of fire. This

situation is typically expected in those situations where the CFRP contribution assumes a significant part of the

member´s resistance (the CFRP increases the original strength significantly).

Under this circumstance, a proper thermal insulation must be displayed. This insulation must comprise insulating

mortars (Sikacrete® 213F) or specific panels which ensure that the temperature in the bonding agent remains

below the softening point. This usually involves a substantial thickness for the insulation.

Sikacrete® 213F

Fire protection mortar.

Cement based, modified with vermiculite.

Spray/Hand application.

Does not contribute to the formation of smoke or toxic fumes.

Typical thickness (CFRP protection): 40mm-60mm(*).

CFRP protection: 45-60 minutes(*).

Fire rating of the protected member: > 4hr(*).

(*)These values may vary significantly according to the characteristics of the RC member and the loads. Contact

Corporate Tech. Dept. for additional info.

Please note that many common solutions for the structural protection in case of fire, based on thin mortar layers

or intumescent coatings, are frequently useless for CFRP laminates, as they are based on thickness with protective

capabilities that are not effective to maintain the temperature of the CFRP adhesive below the critical point.

Even in the case of using protective materials applied in a considerable thickness, the expected protection will be

restricted to a limited period of time (e.g. 45-60 minutes). A long-term protection for the CFRP strengthening (120-

240 minutes) is not feasible unless providing extremely costly or complex solutions. Short term CFRP protections

do not involve a low fire resistance for the structural member.

5 FIRE RESISTANCE

In some situations, the structural member must show a certain fire resistance in case of fire. This fire resistance is

determined by the time (30, 60, 90, 120... minutes) within the load bearing capacity of the member can be

assumed.

This period concerns the necessary time for the evacuation of the building. Hence, the requested fire resistance

according to the local regulations will essentially depend on the occupancy and the distance to the exit, and not on

structural issues.



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The fire resistance concerns the performance of the structural member (e.g. a column, beam) or part of a

structure, and not their constituent materials independently (concrete, steel or CFRP).

Hence, a common mistake associated to the use of bonded CFRP laminates implies that the fire resistance of the

CFRP should meet the resistance time requested for the member, which is not correct (e.g. a 90-minutes rated

column must be able to assume the expected loads for the indicated time, but the individual load bearing capacity

of the concrete, steel and CFRP throughout that period of time are not restricted individually)

As the contribution of the CFRP is expected to be prematurely lost, the strength of the member will basically

depend on the other two components (concrete and steel), which will gradually decrease according to its

temperature. Thus, even when the protective material will only provide a limited additional protection to the CFRP

(1), its effectiveness concerning the protection of the concrete and steel is very significant, therefore the fire rating

of the member can be considerably enhanced (2).



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6 REACTION TO FIRE

In addition to the FIRE RESISTANCE, other major topic is the so called REACTION TO FIRE, which is the

measurement of how a product or system will contribute to the smoke generation, fire development and spread,

particularly in the very early stages of a fire when evacuation is crucial.

The admissible reaction to fire for the materials involved in construction processes is commonly regulated by localcodes, which can even vary among cities located in the same country. The reaction to fire has no relation with the

structural performance of the element.

7 FREQUENTLY ASKED QUESTIONS

Must I necessarily protect the CFRP strengthening against fire?

No. Only in those situations where the mechanical contribution of the CFRP is strictly necessary under the

(reduced) combination of loads corresponding to the fire situation.

The CFRP is not taken into account for this calculation, but this preliminary check must be done in order to verify

the suitability of the CFRP solution.

For an un-protected CFRP strengthening displayed on a beam/column, what´s the expected fire resistance of the

member?

In many cases, the member can exhibit a significant fire resistance (up to 4 hr.), even when the CFRP is lost in case

of fire within the first minutes. The fire resistance of the member is evaluated according to the local or



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international codes (e.g. Eurocode 2 part 1-2 or ACI216.1-07) concerning reinforced concrete members under a fire

situation.

Typically, those codes comprise 3 alternative options that can be considered for the determination of the fire

resistance:

a) Detailed calculation, taken into account the progressive reduction of the strengths for the concrete and the steelthroughout the fire situation.

An accurate calculation can be provided, independently of the characteristics of the member

Complex calculation

b) Simplified calculation, mainly based on the geometry and size of the member, characteristics of the concrete

and the thickness of the concrete cover around the steel bars.

Simple calculation for most of the RC members

The calculation is feasible only in those cases where the RC member meets all the predetermined

conditions for the simplified option (dimensions, concrete cover, etc.)

c) Certification by testing of the RC member

No calculations are necessary. This option is singularly interesting in the case of determining the

performance of a member protected by a certain protective solution.

The certification is only valid for those RC members that meet the same characteristics (geometry, covers,

protective materials…) than those previously evaluated in the test.

In those situations when the mechanical contribution of the CFRP is necessary under a fire situation, what is the

maximum fire resistance we can provide for the CFRP?

In those cases where the un-strengthened member is not able to support the reduced combination of loads in case

of fire, it´s necessary to protect the CFRP laminate in order to maintain its mechanical contribution.

In this case, the maximum achievable protection for the CFRP can be estimated in 60 minutes (Sikacrete® 213F).

However, the Sikacrete® 213F can still protect the remaining components of the RC member (concrete & steel)

beyond this point.

How can I determine if the CFRP must be protected against fire?

This is part of the calculation process, as indicated in the different CFRP guidelines:

.ACI 440.2R-08: section 9.2.1

. fib bulletin 14: sections 3.1.2.5 and 3.2.2

This process must verify if the strength corresponding to the un-strengthened (existing) member exceeds the

expected loads related to the fire situation (no CFRP is involved in this verification, hence the calculation follows

the standard procedures as implemented in Eurocode 2, ACI 318/216 or local codes concerning the calculation of

RC elements)

Is there any certification or test concerning the performance of the protection of the CFRP?

Unlike other materials commonly used for building structures (timber, concrete, steel, etc.), there is not code or

test to determine the performance for the protections in the case of bonded CFRP laminates. This disallows the

possibility to calculate the necessary thickness for the protective material in each situation.



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Alternatively, some tests on strengthened members are feasible, which can evaluate the fire resistance rating for

the protected member (reinforced concrete + external CFRP) in case of fire. Those tests cover some specific

combinations of products, layers, concrete classes, sizes, etc., so they are not valid for members exhibiting sizes or

characteristics different than those tested.

Some certifications comprising Sikacrete® 213F protections for SikaWrap® and Sika® CarboDur® plates have been

done following this philosophy, supplying 4-hour fire resistance rating for the strengthened & protected RCmember (the performance of the CFRP is not evaluated independently of the rest of the RC member).

Underwriters Laboratories of Canada, file BXUVC.N813 – beam strengthened with Sika® CarboDur® plates

and SikaWrap® 103C/230C fabrics.

Underwriters Laboratories of Canada, file BXUVC.N814 – beam strengthened with SikaWrap®

103C/100G/430G fabrics.

Underwriters Laboratories of Canada, file BXUVC.X826 – column strengthened with SikaWrap® 103C fabric.

How long can I protect the CFRP in case of fire?

As indicated previously, there is not any specific standard or code for the determination of the durability of the

CFRP laminates in case of fire.

The protection by means of 40-60mm of Sikacrete® 213F mortar can maintain most of the adhesive´s performance

for a period of time between 45 and 60 minutes. Those values are based on the resulting temperatures

corresponding to real tests, comprising approved fire curves.

The fire rating of the entire member must be calculated independently.

In that case, how can I get 4-hour fire rated column when strengthened by means of CFRP?

The fire rating for a reinforced concrete member essentially depends on its size and the concrete cover of the

reinforcing bars. The presence of the CFRP, even when protected against fire, does not influence the fire resistancecapability of the element beyond the first 45-60 minutes.

Hence, the protection must be focused on the concrete and the steel, as a reduced protective layer will provide a

significant enhancement.

The Sikacrete® 213F mortar, when applied on the surface of the member exposed to the fire (not only on the CFRP

laminate) can provide more than 4-hour fire rating (due to the protection supplied to the concrete and steel

reinforcement), even when the CFRP will not provide any strengthening beyond the first 45-60 minutes.

Can Sika® provide the expected resistance to fire for a strengthened RC member ?

The Sika® CarboDur® software includes a tool to determine if the CFRP must be protected in case of fire. However,we cannot estimate the fire resistance of the member (e.g. 120 minutes) as this is not related to our CFRP

solutions, but regulated by the existing RC standards (e.g. Eurocode 2 or ACI 318/216).



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What are the different possibilities?

Assumption Fire resistance (time) of the

un-strengthened member

Action Achievable fire resistance rating

CFRP not

necessary in case

of fire.

The RC member meets the necessary

resistance to fire (e.g. 90´)

No additional measure is

needed

15-240 minutes, according to the characteristics

of the RC member

CFRP not

necessary in case

of fire.

The RC member does not meet the

necessary resistance to fire (e.g. 90´)

Protection for the RC

member

15-240 minutes, according to the characteristics

of the RC member and the complementary

protection

CFRP is necessary

in case of fire.

The RC member cannot meet the

necessary resistance to fire

Sikacrete® 213F

protection for the CFRP

and RC member

≤ 60 minutes.

Can I use an intumescent coating for the protection of the CFRP?

No.Intumescent coatings are based on the insulation capability of the coating after its swelling/foaming process, as a

result of heat exposure. This swelling is expected at a relatively high temperature, hence the adhesives used for

the display of the CFRP result damaged or destroyed previously.

My customer claims that he knows a protective mortar for reinforced concrete structures, able to provide 240

minutes protection by means of a single layer of 20mm. Is this also valid for the CFRP?

No.

Concrete and steel maintain most of their mechanical properties even at high temperatures (e.g. 400ºC). Hence,

it´s relatively easy to limit the temperature in the concrete surface bellow this point by means of a small insulation

thickness. However, the maximum temperature for the CFRP is much more restrictive, hence a 20mm layer will

simply protect the CFRP for a few minutes (10-15 minutes?).

What is the maximum admissible temperature for the CFRP in case of fire?

The carbon fiber filaments are able to resist high temperatures. Pultruded plates (e.g. Carbodur plates and rods)

also exhibit a remarkable thermal resistance (>100ºC) due to the manufacturing process.

Hence, the performance of the CFRP system will be limited by the softening of the adhesive (Sikadur® XXX) used

for the adhesion and/or saturation of the CarboDur®/SikaWrap®

Most of the existing guidelines concerning the design of CFRP strengthening solutions take the Tg (glass transition

temperature) as the limit value to be considered. That information can be obtained from the adhesive´s PDS.However, one has to consider that Tg may significantly vary due to the curing conditions during the application or

as a consequence of long-term environmental parameters.

We need to provide a solution regarding the seismic retrofitting for a building structure. Do we need to protect

the CFRP against fire?

No.

The need for the CFRP strengthening is limited to acting loads as a consequence of the seismic accelerations, which

may occur during a few minutes in a decade or a century.



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However, the possibility of experiencing a fire and an earthquake simultaneously is almost negligible.

A fire situation can be expected AFTER the earthquake, when the CFRP is useless, hence the un-strengthened

structure is able to support the expected loads, even if the CFRP is lost due to the fire.

A passive fire protection system (e.g. Sikacrete® 213F) ensures that the structure will not be damaged in case of

fire, right?

No.

It simply ensures that the structural member will not collapse during the evacuation of the building (fire resistance

rating), even when the part of the concrete and steel may result damaged.

If the fire situation continues beyond this point, the structure will be significantly damaged and may even collapse,

independently of the protection.

The passive fire protection for the CFRP (e.g. Sikacrete® 213F) ensures that the CFRP strengthening will not be

damaged in case of fire, right?

This can be expected only in those cases where the temperature in the adhesive does not exceed a moderatetemperature (60-70 ºC max.), which is not realistic unless in the case of small fires that are extinguished in a short

period of time.

Hence, in the case of significant fires, the CFRP system will be finally damaged even when protected, and should be

replaced subsequently.

How can I know the requested fire rating (time) for a certain structure?

Even when the method for the determination of the resistance to fire for RC structures can be easily found in local

or international codes (Eurocode/ACI), the necessary fire resistance ratings according the different situations are

generally defined in the local regulations (national, regional or even municipal).

Hence, a 4-storey residential building located in the “X” city may need 60 minutes fire rating, and a similar building

in the “Y” city may need 90 minutes (even when “X” and “Y” are located in the same country!).

Do bridges follow the same restrictions than buildings concerning the protection of CFRP?

Usually not.

As indicated, the fire rating of the structure is mainly oriented to the evacuation of the people.

Unlike the building structures, where the evacuation may take several hours, the fire resistance rating for bridges

may be not regulated or even not necessary as the evacuation and un-loading of the bridge structures is usually

simple.

However, this must be verified according to the local codes.

8 REMARKS

The information supplied in the different examples and graphs, concerning the performance of the protective

systems, fire ratings, time expectancies, etc. correspond to real situations. However, the need for a fire-protection

system and its performance depends on multiple variables related to the characteristic of the RC member and its

anticipated loads; hence every solution must be verified independently.

For further information, please contact David Vázquez.

mailto:[email protected]






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9 LEGAL NOTE

The information, and, in particular, the recommendations relating to the application and end-use of Sika products, are given in good faith

based on Sika's current knowledge and experience of the products when properly stored, handled and applied under normal conditions in

accordance with Sika’s recommendations. in practice, the differences in materials, substrates and actual site conditions are such that no

warranty in respect of merchantability or of fitness for a particular purpose, nor any liability arising out of any legal relationship whatsoever,

can be inferred either from this information, or from any written recommendations, or from any other advice offered. The user of the product

must test the products suitability for the intended application and purpose. Sika reserves the right to change the properties of its products. The

proprietary rights of third parties must be observed. All orders are accepted subject to our current terms of sale and delivery. Users must

always refer to the most recent issue of the local Product Data Sheet for the product concerned, copies of which will be supplied on request.

10 KEY WORDS

Sika Carbodur, SikaWrap, fire situation, fire, fire rating, Sikacrete 213F, fire resistance, reaction to fire.

SIKA SRVICES AG

Corporate Technical Dept.

Aragoneses 17

28108, Alcobendas

Spain

www.sika.com

Version given by

David Vázquez

Phone: +34 91 657 23 75

Fax:

Mail: [email protected]

design and protection in case of fire (sikawrap and sika carbodur)

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