Effect of Using Bracing Members in Reducing Thermal Effects in Long Buildings

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1-Introduction
Thermal expansion joints in buildings may be determined initially on an empirical basis .If results are deemed by designer to be too conservative or if the empirical approach is not sufficiently to be applicable to the type of structure being investigated, a more precise analysis should be undertaken (Hendry A.W.,2003) .As empirical basic, Table (3) is published by the ACI committee 224-3R-95 . In this Table spacing of expansion joint are range from (9-60) m depending on the type of structure. As an alternative to the empirical basics, Martin and Acosta (1970) present an analytical method for calculating the maximum spacing of expansion joints in onestory frame with nearly equal spans (ACI 224 .3R-1995). From the chart proposed from Martin and Acosta, the maximum spacing of expansion joint is 130 m. To avoid damage of external wall, Martin and Acosta limited the maximum allowable lateral deflection to (h/180 ), while the lateral deflection for masonry structure is limited to (0.002) times the floor high by professor Schierle (AL-Sharmani,2007 ) .In this research, two criterion are considered, the value of reinforcement in beams and the lateral deflection of the structure, therefore the principle goal from this research is to study the effect of long building construction without expansion joints on its structural behavior

Changes
As in most structural problems, the investigation of the thermal effects is reduced to basic understanding of distributed forces and deformation within the structure. If deformations are resisted the resulting force system in structural members may exceed the members , strength and cause structural failure: if they are not resisted the change of geometry in the structure may interfere with its overall performance. Therefore, the designer ' s task is to select one of the following three board basic approaches (the national academy of sciences,1974 ).
1. Limit the potential for deformation in the structure (without causing failure) by designing the appropriate members to be substantially stiffened and strengthened.
2. Allow substantial movement of the building ' s structural and nonstructural components will not be adversely affected. Such a structure will require partially no additional strength of members to withstand thermal effects.
3. Strike a compromise between capacity to resist stress and ability to withstand deformation without sacrificing building performance.
In the present research, the first point is adopted and the movement due to temperature is prevented by using bracing beams to increase the strength of structure

3-Computation of Design Temperature Change ( Thermal Load)
Since construction is carried out over considerable period, the various element of the structure are installed at different temperatures. The temperature changes causing displacements and stresses in structure are changes from theses installation/erection temperatures, over which the designer has little, if any, control. Yet while it is apparent that temperature change is one of the most important factors influencing the potential linear expansion /contraction of a building, there is no possibility of establishing exactly the maximum expected temperature change because this change is not the same for all parts of the structure and is not known during the design phase for any one particular part of the structure. From the above reasons the national academy of sciences ,1974, was developed the following guidelines to serve as an aid to computation of design temperature change : • It should be assumed that structures will be built when the minimum daily temperature are above 32 F ( 0 0 C)) • Mean temperature (Tm) should be based on only the construction season(the contiguous period during which the minimum daily temperature is above 32 F).
• The anticipated high-temperature extreme (Tw) should be considered as the temperature that is exceed, on the average, only 1 percent of the time during the summer months ( June through September) in the locality of the building . • The anticipated low-temperature extreme ( Tc) should be considered as the temperature that is equaled or exceed, on the average, 99 percent of the time during the winter months ( December through February ) in the locality of the building. • Using the data described above, the design temperature change ( t ) can be uniquely defined according to t =(Tw -Tm )or (Tm -Tc ) whichever is greater.

4-Computer Analysis 4-1 STAAD.pro 2004 Software
The structural analysis and design program is the most popular structural software in Iraq; it is used in most of the structural consulting offices and Universities of Iraq. This program is used in analysis and design of all types of structural systems and materials, this program is used as the main tool in this investigation.

4-2 Data Analysis 4-2-1 Load
Two types of load are used in the analysis; gravity load and thermal load .Wind Whichever is greater.
. The value of Tw, Tm and Tc for Al-Najaf city are calculate according to statistical data (Table,4 program under the field of temperature change of axial elongation

4-2-2 Geometry and Materials
One-story reinforcement concrete building 150 m long is investigated in this research. The cross-sectional elevation of the chosen building is shown in Fig. (2).

Assumption
• All beams are of same size (500 x 250) mm.
• All columns are of same size (400x 250) mm.
• High of building is 4 m • Compressive strength of concrete is (21.7) N /mm 2 .

5-Results of the Analysis and Design
As mentioned in the abstract, three case studies are done in this research to study the effect of bracing beams on a structure subjected to constant temperature equals 19 0 C, which represents the design temperature change for Al-Najaf city calculated according to guidelines of the national academy of sciences, 1974. Table (1) shows the results of the analysis and design of these cases.
To development the present study, the same restrained structure is subjected to different temperatures ranging from (19-40) 0 C. In 40 0 C the lateral displacement of the structure nearly reaches the allowable value that proposed by professor Schierle.
Table (2) shows results of the analysis and design of this case. .

6-Discussion of Results
From table (1), the axial load in beams is the largest variable in the three cases studies, Fig.(1) shows the axial forces in these case studies. Results in table (1)  From Table (2 ), as a result to increase in the temperature change from (19-40) 0 C, moments in beams are increased by 20% , the axial forces are increased by 83% and the ratio of reinforcement is increased by 291%. For columns , moments are increased by 131%.The lateral displacement for the structure is increased by 134%.
From results above, we can conclude that the lateral displacement reaches to the allowable displacement in 40 0 C, but the beams in this temperature need to strengthen according to the high ratio of reinforcement required. In all temperature changes except 19 0 C, beams need to strengthen

5-Conclusions and Recommendations
In the present study, the following points has bean concluded: 1-To analyze long building, thermal loads must be applied in the same time with other types of a loading.
2-Using the analytical method instead of empirical approach to determination numbers and locations of expansion joints for the buildings is more exact.
3-Using the structural solutions like the bracing beams is suitable to construction a reinforced one-story building subjected to 19 0 C without expansion joints for length equals 150 m .