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Load combination for Temp.Analysis
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paravansefi
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Joined: 17 Jan 2009
Posts: 32

PostPosted: Mon Feb 02, 2009 8:42 am    Post subject: Load combination for Temp.Analysis Reply with quote

Dear all,

What are the load factors that are to be used for doing the temp. analysis?
And the combinations with other load cases?

I.S.875 does not specify this in detail.

Pls. help,

regards,
Aravan
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paravansefi
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Joined: 17 Jan 2009
Posts: 32

PostPosted: Tue Feb 03, 2009 10:27 am    Post subject: Temperature load combinations Reply with quote

Dear Mr.Alok,

Let me quote one of your posting relate to the temperature load combinations.

The point you mentoned is that the temperature forces are to be considered only for the serviceability check.

But then how do we include the load factors when we combine this with other load cases?
Pls. explain in detail.,

regards,
Aravan.





Dear All,

Temperature induced forces are to be considered for SLS (i.e. Serviceability
Limit State) checks only. Under ULS (i.e. Ultimate Limit State) checks,
temperature forces are to be ignored (Since cracking of structure will
dissipate the thermal induced forces).

For SLS checks, the annual(seasonal) variation in temperature shall be taken
in the analysis. The magnitude of forces shall be reduced to half to take
into account the effect of sympathetic creep.

As far as temperature differential is concerned, the same shall be
considered as an instantaneous effect, without taking any relief due to
creep.

Load Combination with temperature gradient : Only a fraction of
characteristic live load shall be considered in combination with
Temperature. The magnitude is different in different codes (i.e. It is 50%
in case of IRC code and 60% in case of Euro Code EC2, when temperature is an
accompanying load).

Best wishes

Alok Bhowmick
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ibarua
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Joined: 26 Jan 2003
Posts: 1039

PostPosted: Tue Feb 03, 2009 12:11 pm    Post subject: Load combination for Temp.Analysis Reply with quote

3rd Feb 2009

It's improbable - statistically speaking -- that maximum temperature effect will occur together with design eq. or design wind load.

Indrajit Barua.

On Tue, 03 Feb 2009 paravansefi wrote :
Quote:
Dear Mr.Alok,

Let me quote one of your posting relate to the
temperature load combinations.

The point you mentoned is that the temperature forces
are to be considered only for the serviceability check.

But then how do we include the load factors when we
combine this with other load cases?
Pls. explain in detail.,

regards,
Aravan.





Dear All,

Temperature induced forces are to be considered for SLS
(i.e. Serviceability
Limit State) checks only. Under ULS (i.e. Ultimate
Limit State) checks,
temperature forces are to be ignored (Since cracking of
structure will
dissipate the thermal induced forces).

For SLS checks, the annual(seasonal) variation in
temperature shall be taken
in the analysis. The magnitude of forces shall be
reduced to half to take
into account the effect of sympathetic creep.

As far as temperature differential is concerned, the
same shall be
considered as an instantaneous effect, without taking
any relief due to
creep.

Load Combination with temperature gradient : Only a
fraction of
characteristic live load shall be considered in
combination with
Temperature. The magnitude is different in different
codes (i.e. It is 50%
in case of IRC code and 60% in case of Euro Code EC2,
when temperature is an
accompanying load).

Best wishes

Alok Bhowmick








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biju
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Joined: 26 Jan 2003
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Location: Mumbai

PostPosted: Tue Feb 03, 2009 2:09 pm    Post subject: Load combination for Temp.Analysis Reply with quote

Dear all,

Temperature load should be combined with all other load cases.
I think the factor also should be the same, ie whatever is applicable for lateral loads.

regards,

Biju.




"ibarua" <forum@sefindia.org>  
03/02/2009 06:39 PM    Please respond to
general@sefindia.org

To
general@sefindia.org   cc
Subject
[SEFI] Re: Load combination for Temp.Analysis




3rd Feb 2009

It's improbable - statistically speaking -- that maximum temperature effect will occur together with design eq. or design wind load.

Indrajit Barua.

On Tue, 03 Feb 2009 paravansefi wrote :   --auto removed--

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bsec
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PostPosted: Wed Feb 04, 2009 3:00 pm    Post subject: Load combination for Temp.Analysis Reply with quote

Dear Aravan,

If you refer to the BIS code (i.e. IS:875), the thermal forces are shown as combined with other loads with load factor of 1.0. However I am of the view that this load combination in IS:875 is outdated and badly requires revision. I agree with Mr Barua that thermal loads should not be combined with EQ loads.  

Reasons for not considering thermal stresses, generally is that in a reinforced concrete structure, once cracking is permitted under ultimate limit state, it relieves all the eigenstresses generated due to temperature. However under SLS, it is important to ensure that the crack width is controlled and hence SLS check is important.  

As per the Euro codes, the thermal forces are considered only under SLS load combination and for checking of equilibrium.  Load factor considered is 1.0 in case temperature loading is the ‘dominant’ load and 0.6 or 0.5 in case temperature load is the ‘associated’ load (Those not conversant with Eurocode may find it difficult to understand).  

As per the present IRC codes, which are based on working stress approach, the thermal loads are taken in combination with EQ as well as other loads. However 15% overstressing is permitted under load combination with temperature (excluding wind / EQ), 50% overstressing is permitted for load combination with EQ & 33% overstressing is permitted for load combination with Wind. However the present IRC codes are under revision and the revised codes are being drafted in line with Eurocodes.

With best wishes

Alok Bhowmick






-----Original Message-----
From: paravansefi [mailto:forum@sefindia.org]
Sent: Tuesday, February 03, 2009 3:57 PM
To: general@sefindia.org
Subject: [SEFI] Re: Load combination for Temp.Analysis

Dear Mr.Alok,

Let me quote one of your posting relate to the temperature load combinations.

The point you mentoned is that the temperature forces are to be considered only for the serviceability check.

But then how do we include the load factors when we combine this with other load cases?
Pls. explain in detail.,

regards,
Aravan.





Dear All,

Temperature induced forces are to be considered for SLS (i.e. Serviceability
Limit State) checks only. Under ULS (i.e. Ultimate Limit State) checks,
temperature forces are to be ignored (Since cracking of structure will
dissipate the thermal induced forces).

For SLS checks, the annual(seasonal) variation in temperature shall be taken
in the analysis. The magnitude of forces shall be reduced to half to take
into account the effect of sympathetic creep.

As far as temperature differential is concerned, the same shall be
considered as an instantaneous effect, without taking any relief due to
creep.

Load Combination with temperature gradient : Only a fraction of
characteristic live load shall be considered in combination with
Temperature. The magnitude is different in different codes (i.e. It is 50%
in case of IRC code and 60% in case of Euro Code EC2, when temperature is an
accompanying load).

Best wishes

Alok Bhowmick

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paravansefi
SEFI Regulars
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Joined: 17 Jan 2009
Posts: 32

PostPosted: Thu Feb 05, 2009 11:25 am    Post subject: Load combination for Temp.Analysis Reply with quote

Dear Mr.Alok,

Expressing deep gratitude for your elaborate reply.

But the following points are still not clear to me.
1.How do we check for SLS like crack width if I am using a commercial software?
2.So for Limit state of collapse, temp. need not be considered?

3. In that case, Exp. joints are mandatory for long bldgs. Because we cannot capture the temp. stresses in the design.Pls. clarify


regads,

Aravan.

On Wed, 04 Feb 2009 bsec wrote :
Quote:
Dear Aravan,

If you refer to the BIS code (i.e. IS:875), the thermal forces are shown as combined with other loads with load factor of 1.0. However I am of the view that this load combination in IS:875 is outdated and badly requires revision. I agree with Mr Barua that thermal loads should not be combined with EQ loads.

Reasons for not considering thermal stresses, generally is that in a reinforced concrete structure, once cracking is permitted under ultimate limit state, it relieves all the eigenstresses generated due to temperature. However under SLS, it is important to ensure that the crack width is controlled and hence SLS check is important.

As per the Euro codes, the thermal forces are considered only under SLS load combination and for checking of equilibrium. Load factor considered is 1.0 in case temperature loading is the dominant load and 0.6 or 0.5 in case temperature load is the associated load (Those not conversant with Eurocode may find it difficult to understand).

As per the present IRC codes, which are based on working stress approach, the thermal loads are taken in combination with EQ as well as other loads. However 15% overstressing is permitted under load combination with temperature (excluding wind / EQ), 50% overstressing is permitted for load combination with EQ & 33% overstressing is permitted for load combination with Wind. However the present IRC codes are under revision and the revised codes are being drafted in line with Eurocodes.

With best wishes

Alok Bhowmick








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bsec
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PostPosted: Thu Feb 05, 2009 12:19 pm    Post subject: Load combination for Temp.Analysis Reply with quote

Dear Aravan,

You asked : “How do we check for SLS like crack width if I am using a commercial software?”

Reply : Commercial softwares have provision for taking temperature loads. Use un cracked section properties of structural members for analysis and check crack width for the design. The crack width should be within the permissible limit.

You asked : “So for Limit state of collapse, temp. need not be considered?”

Reply : Yes

You asked “In that case, Exp. joints are mandatory for long bldgs. Because we cannot capture the temp. stresses in the design.Pls. clarify”

Reply : Expansion joints are necessary for long buildings to control the crack widths within limits.  

With best wishes

Alok Bhowmick

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hemant324
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Joined: 14 Feb 2013
Posts: 6

PostPosted: Tue Oct 10, 2017 7:43 am    Post subject: Re: Load combination for Temp.Analysis Reply with quote

Dear Alok,

You mentioned that thermal loads are considered under SLS load combination. Can you provide any reference to this statement.

My query is for steel structure and is located in Kuwait.
Another question is whether we need to combine temperature load with wind load.
Thanks for sharing knowledge.

bsec wrote:
Dear Aravan,
If you refer to the BIS code (i.e. IS:875), the thermal forces are shown as combined with other loads with load factor of 1.0. However I am of the view that this load combination in IS:875 is outdated and badly requires revision. I agree with Mr Barua that thermal loads should not be combined with EQ loads.  

Reasons for not considering thermal stresses, generally is that in a reinforced concrete structure, once cracking is permitted under ultimate limit state, it relieves all the eigenstresses generated due to temperature. However under SLS, it is important to ensure that the crack width is controlled and hence SLS check is important.  

As per the Euro codes, the thermal forces are considered only under SLS load combination and for checking of equilibrium.  Load factor considered is 1.0 in case temperature loading is the ‘dominant’ load and 0.6 or 0.5 in case temperature load is the ‘associated’ load (Those not conversant with Eurocode may find it difficult to understand).  

As per the present IRC codes, which are based on working stress approach, the thermal loads are taken in combination with EQ as well as other loads. However 15% overstressing is permitted under load combination with temperature (excluding wind / EQ), 50% overstressing is permitted for load combination with EQ & 33% overstressing is permitted for load combination with Wind. However the present IRC codes are under revision and the revised codes are being drafted in line with Eurocodes.

With best wishes

Alok Bhowmick






-----Original Message-----
From: paravansefi [mailto:forum@sefindia.org]
Sent: Tuesday, February 03, 2009 3:57 PM
To: general@sefindia.org
Subject: [SEFI] Re: Load combination for Temp.Analysis

Dear Mr.Alok,

Let me quote one of your posting relate to the temperature load combinations.

The point you mentoned is that the temperature forces are to be considered only for the serviceability check.

But then how do we include the load factors when we combine this with other load cases?
Pls. explain in detail.,

regards,
Aravan.





Dear All,

Temperature induced forces are to be considered for SLS (i.e. Serviceability
Limit State) checks only. Under ULS (i.e. Ultimate Limit State) checks,
temperature forces are to be ignored (Since cracking of structure will
dissipate the thermal induced forces).

For SLS checks, the annual(seasonal) variation in temperature shall be taken
in the analysis. The magnitude of forces shall be reduced to half to take
into account the effect of sympathetic creep.

As far as temperature differential is concerned, the same shall be
considered as an instantaneous effect, without taking any relief due to
creep.

Load Combination with temperature gradient : Only a fraction of
characteristic live load shall be considered in combination with
Temperature. The magnitude is different in different codes (i.e. It is 50%
in case of IRC code and 60% in case of Euro Code EC2, when temperature is an
accompanying load).

Best wishes

Alok Bhowmick

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hemal
...
...


Joined: 01 Apr 2008
Posts: 126

PostPosted: Tue Oct 10, 2017 7:12 pm    Post subject: Reply with quote

ACI 318-2014 requirement for combining self straining loads (creep, shrinkage, temperature etc) with other load is attached here.


ACI 318-2011 have similar requirement as that of ACI 318-2014. As an alternative to that it has following load combinations

1) 0.75 (1.4D+1.7L+1.4T)
2) 1.4(D+T)

However, above load combinations are removed in ACI-318-2014 and now it has requirement as attached only.



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hemant324
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Joined: 14 Feb 2013
Posts: 6

PostPosted: Wed Oct 11, 2017 3:16 am    Post subject: Re: Load combination for Temp.Analysis Reply with quote

hemant324 wrote:
Dear Alok,


My query is related to Euro Codes -
1) Temperature load is to be considered for SLS case only?
2) Do we need to apply temperature and wind load simultaneously?


where can I find references to these statements in Eurocode?






You mentioned that thermal loads are considered under SLS load combination. Can you provide any reference to this statement.
My query is for steel structure and is located in Kuwait.
Another question is whether we need to combine temperature load with wind load.
Thanks for sharing knowledge.

bsec wrote:
Dear Aravan,
If you refer to the BIS code (i.e. IS:875), the thermal forces are shown as combined with other loads with load factor of 1.0. However I am of the view that this load combination in IS:875 is outdated and badly requires revision. I agree with Mr Barua that thermal loads should not be combined with EQ loads.  

Reasons for not considering thermal stresses, generally is that in a reinforced concrete structure, once cracking is permitted under ultimate limit state, it relieves all the eigenstresses generated due to temperature. However under SLS, it is important to ensure that the crack width is controlled and hence SLS check is important.  

As per the Euro codes, the thermal forces are considered only under SLS load combination and for checking of equilibrium.  Load factor considered is 1.0 in case temperature loading is the ‘dominant’ load and 0.6 or 0.5 in case temperature load is the ‘associated’ load (Those not conversant with Eurocode may find it difficult to understand).  

As per the present IRC codes, which are based on working stress approach, the thermal loads are taken in combination with EQ as well as other loads. However 15% overstressing is permitted under load combination with temperature (excluding wind / EQ), 50% overstressing is permitted for load combination with EQ & 33% overstressing is permitted for load combination with Wind. However the present IRC codes are under revision and the revised codes are being drafted in line with Eurocodes.

With best wishes

Alok Bhowmick






-----Original Message-----
From: paravansefi [mailto:forum@sefindia.org]
Sent: Tuesday, February 03, 2009 3:57 PM
To: general@sefindia.org
Subject: [SEFI] Re: Load combination for Temp.Analysis

Dear Mr.Alok,

Let me quote one of your posting relate to the temperature load combinations.

The point you mentoned is that the temperature forces are to be considered only for the serviceability check.

But then how do we include the load factors when we combine this with other load cases?
Pls. explain in detail.,

regards,
Aravan.





Dear All,

Temperature induced forces are to be considered for SLS (i.e. Serviceability
Limit State) checks only. Under ULS (i.e. Ultimate Limit State) checks,
temperature forces are to be ignored (Since cracking of structure will
dissipate the thermal induced forces).

For SLS checks, the annual(seasonal) variation in temperature shall be taken
in the analysis. The magnitude of forces shall be reduced to half to take
into account the effect of sympathetic creep.

As far as temperature differential is concerned, the same shall be
considered as an instantaneous effect, without taking any relief due to
creep.

Load Combination with temperature gradient : Only a fraction of
characteristic live load shall be considered in combination with
Temperature. The magnitude is different in different codes (i.e. It is 50%
in case of IRC code and 60% in case of Euro Code EC2, when temperature is an
accompanying load).

Best wishes

Alok Bhowmick

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