In this study, fire resistance tests were performed on a conventional slim floor beam and a prestressed composite beam with corrugated webs, which is suitable for a long-span structure with a reduction in story height by utilizing the prestress and accordion effect. In the fire test program, the ISO 834 standard fire curve was adopted. Key test variables were the effect of prestress, shape of corrugated webs, and thickness of sprayed fireproofing material. All of the test specimens demonstrated enhanced fire resistance performance exceeding the expected performance level. The prestressed composite beams with corrugated webs especially showed excellent fire performance, considering these specimens had thin fireproofing thickness compared to the conventional slim floor specimen

Cho, Bum-Yean

Kim, Heung-Youl

Kim, Hyung-Jun

Park, Kyung-Hoon

English

Purdue E-Pubs

105 10th International Conference of the International Institute for Infrastructure Resilience and Reconstruction (I3R2) 20–22 May 2014 Purdue University, West Lafayette, Indiana, USA Experimental Study on the Fire Resistance Performance of Prestressed Composite Beam with Corrugated Web under Standard Fire with Loading Condition Heung-Youl Kim, Hyung-Jun Kim, Kyung-Hoon Park, and Bum-Yean Cho Fire Research Center, Korea Institute of Construction Technology ABSTRACT In this study, fire resistance tests were performed on a conventional slim floor beam and a prestressed composite beam with corrugated webs, which is suitable for a long-span structure with a reduction in story height by utilizing the prestress and accordion effect. In the fire test program, the ISO 834 standard fire curve was adopted. Key test variables were the effect of prestress, shape of corrugated webs, and thickness of sprayed fireproofing material. All of the test specimens demonstrated enhanced fire resistance performance exceeding the expected performance level. The prestressed composite beams with corrugated webs especially showed excellent fire performance, considering these specimens had thin fireproofing thickness compared to the  conventional slim floor specimen. 1. INTRODUCTION Currently, the demand for longer spans and to reduce the height of the buildings is increasing as buildings are built on a larger scale and are high rises. Therefore, although many studies are conducted on the effectiveness of the new composite beam, the development of the composite beam fails to be effective for reducing building height and being used for long-span structures (Kim, Lee, Choi, Choi, & Jung, 2011; Oh Lee, & Kim, 2012). Recently, long-span composite beams with various shapes have been reviewed; the weak point of steel members and reinforced concrete have been complemented. (Kim & KIM, 2012) Therefore, prestressed composite beams with corrugated web have been proposed to obtain the proper structure type for reducing building height and increasing its long span, as shown in Figure 1 in the previous study of the authors. The purpose of the proposed composite beam is to increase the introduction efficiency of prestress by using stress concentration in the upper and lower flange as much as possible, known as the accordion effect, by introducing corrugated web to improve the poor introduction efficiency of prestressing caused by high axial rigidity of the existing I-type and composite sections (Abbas, Sause, & Driver, 2007). Also, steel beams with the corrugated web are embedded into the concrete. Therefore, the composite capacity can be increased by securing the additional bearing area caused by the increase in contact area with the concrete by the height of corrugated web in the bond stress generated between the existing steel and concrete. In addition, it can be highly effective by preventing the local buckling which is the disadvantage of composite beams with corrugated web through the composition of the concrete. However, the current design criteria demand a proper level of fire resistance performance for all the structures. Therefore, in the study, a fire resistance performance experimentas w carried out to evaluate the fire resistance performance for composite beams with the corrugated web developed in the previous study. In particular, the major experiment factors were the introduction of prestress, shape of the corrugated web, and the depth of the fire resistance cover; the performance was evaluated in accordance with the ISO 834 Standard Fire Curve. 2. EXPERIMENT PLAN 2.1. General Experiment The fire resistance experiment was carried out, depending on the shape of the section and the fire resistance cover depth in the lower part of the beam, to evaluate the fire resistance performance of the composite beam with the corrugated web introducing the PS. The  fire  resistance performance for  the    Figure 1. Description on prestressed composite beam with corrugated webs 106 composite beam with the corrugated web was analyzed by dividing the two-layer corrugated web and one-layer corrugated web, as shown in Figure 2. In particular, the fire resistance cover material hydrometallurgy pearlite was sprayed during the construction to secure the required fire resistance performance based on existing case studies. The fire resistance experiment was carried out for the minimum section to satisfy the fire resistance performance for over two hours under the noncovered condition based on the results of the structure experiment and numerical analysis in the air temperature. In addition, the specimen was fabricated with a 7.5 m heating face and a 7.7 m length to analyze the fire resistance performance for the long-span composite beam. 2.2. Materials 2.2.1. Steel An H-shape beam used in the study was fabricated with SS400 steel. The mechanical properties of SS400, the steel member for the architectural structure, are regulated, as shown in Table 1 (KS D3503, Rolled Steels for General Structure).  2.2.2. Concrete 24 MPa concrete was applied to the fabrication of the composite beam; the measurement result on the compressive strength of the concrete specimen is shown in Table 2. 2.2.3. Cover Material for Fire Resistance The fire resistance cover material hydrometallurgy pearlite was sprayed for the fire resistance cover of the steel member exposed in the lower part of the composite beam. For the cover material, E product of K company was used, which has been accredited for the fire resistance. The cover depth in each required fire resistance performance is shown in Table 3 in case the product is applied to the beam. 2.3. Fabrication Details of the Specimen To evaluate the fire resistance performance of the composite beam with the PS corrugated web under a standard fire with loading conditions, the specimen was composed, as shown in Table 4. The corrugated web is divided into the two-layer web [S-1] and one-layer web [S-2]. The fire resistance performance was compared depending on the type of the web. In the previous study, there were 89 minutes of fire resistance performance in the specimen with the same section size in the noncovered condition. Therefore, the composite beam of the corrugated web was sprayed with 19 mm (for 2 hours) for the two-layer web and 9 mm (for 1 hour) for the one- layer web to secure the fire resistance performance for 3 hours, considering the accordion effect caused by the corrugated web. The specimen with the minimum size of the section [S-3] was fabricated considering the structure performance of the one-layer web composite beam in the air temperature to verify the fire resistance performance under the noncovered condition.   (a) 1Layer (b) 2Layer Figure 2. The shape of corrugated web  Table 1. The results of the tensile test Type Spec. Testing Method Testing Result Test Yield strength (MPa) ≥ 245 KS B 0802 251 Tensile strength (MPa) 400–510 422 elongation (%) ≥ 20 29  Table 2. The resultsof the concrete test Type Spec. Testing Method Testing Result Test Compression strength (MPa) ≥ 24 KS F 2405 26  Table 3. Mixing ratio of concrete Fire resistance performance Thickness (㎜) 1 hour 9 2 hour 19  Table 4. Composition of specimen Specimen Parameter Thickness of covering material (㎜) H-beam Size (㎜) S-1 2 layer corrugated web 19 360×236 ×346×14×22 S-2 1 layer corrugated web 9 S-3 1 layer corrugated web - 320×236 ×346×14×22  107 2.4. Experiment Method The fire resistance experiment has been carried out in accordance with the KS F 2257-5, Fire Resistance Experiment Method of Architectural Member-Performance Condition of Parallel Internal Force District Member. The fire resistance experiment was carried out under the uniformly distributed loading condition, as shown in Figure 4. The design load and loading condition of the specimen is shown in Table 5. The evaluation of the fire resistance performance under the loading condition is carried out by the deformation, and its rate is in accordance with KS F 2257-1, Fire Resistance Experiment Method of Architectural Member–General Requirement. It is considered as nonresponsive status only if it exceeds both standards of the deformation (Equation 1) and its rate (Equation 2). Since the shape can be rapidly and relatively deformed until reaching a stable status, the performance standard of the deformation is not applied until the deformation exceeds L/30. Deformation    :    (1) Deformation rate:   (2) Where L is the span of a specimen (mm), and d is the distance between the location for the maximum compressive force of the structure section and the location for the maximum tensile strength (mm). 3. EXPERIMENT RESULT As a result of the fire resistance experiment, depending on the type of web and cover depth, it was shown that over 180 minutes of fire resistance performance could be secured for S-1 and S-2. For S-1, a -82.2 mm deformation and -0.70 mm/min deformation rate were seen at 180 minutes, the end of the fire resistance experiment. For S-2, a -73.6 mm deformation and -0.28 mm/min deformation rate were Table 5. Design load and loading condition for fire test Specimen Design Load (ton) Load Ratio Test Load (ton) S-1, S-2, S-3 82.7 0.4 33.1   Figure 4. Testing setup  Table 6. Fire resistance performance by displacement and rate of displacement Specimen Time (min) Displacement (mm) Rate of displacement (mm/min) Fire resistance (min) S-1 60 -24.9 -0.08 180 120 -50.0 -0.66 180 -82.2 -0.70 S-2 60 -25.4 -0.04 180 120 -48.5 -0.16 180 -73.6 -0.28 S-3 60 -212.0 -0.3 138 120 -255.8 -3.0 139 -402.3 -49.8  seen. For S-3, the fire resistance performance was lost because the deformation and its rate exceeded the limit value at 139 minutes after starting the experiment. According to the fire resistance performance standard, for S-1 and S-2, the standard for the deformation was -325.1 mm, and the deformation rate was -14.4 mm/min. For S-3, the standard for the deformation was -378.1 mm, and the deformation rate was -16.8 mm/min. Specimen S-1 S-2 S-3 Section   Elevation  Figure 3. Drawing of specimen 108  Figure 5. Displacement of long span composite beam For S-1 and S-2, 25.3% and 22.6%, respectively, were deformed based on the standard of the allowable deformation limit. Fire resistance performance for S-1 and S-2 was similar. However, considering S-1 used 2 times the fire resistance cover material compared to S-2, it is considered that one-layer corrugated web is more effective than the two-layer corrugated web for the ease of the stress concentration in the upper and lower part of flange caused by the accordion effect. Although noncovered conditions and minimum section size conditions were applied to S-3, the fire resistance performance was secured at 138 minutes. The deformation depending on the time in each specimen is shown in Figure 5. 4. CONCLUSION In this study, the web shape and the fire resistance cover depth were used as the major factors to evaluate the fire resistance performance of the composite beam; based on that, the experiment could reach a conclusion as follows. 1. For the two-layer corrugated web, a hollow space was formed inside the beam so that the high deformation was generated under the loading condition. For the corrugated web, it is considered that the improved fire resistivity was shown by blocking the effect mentioned. 2. As a result of the fire resistance experiment using the actual loading, it was shown that the specimen of the composite beam applying the fire resistance cover material fully satisfied the standard of bending performance (deformation and its rate) for 3 hours exposed to the fire limited in accordance with ISO 834-1. 3. Although the size of the section was minimized and fire resistance cover material was not used, the fire resistance performance was secured for 138 minutes. It can be concluded that the fire resistance performance can be secured for over 3 hours with no cover which can be applied to the actual site by adjusting the size of section and type of the corrugated web. REFERENCES Abbas, H. H., Sause, R., & Driver, R. G. (2007). Analysis of flange transverse bending of corrugated web I-girders under in-plane loads. Journal of Structural Division, 133(3), 347–355. http://dx.doi.org/10.1061/(ASCE)0733-9445(2007) 133:3(347)  Kim. H. J., & Kim H. Y. (2012). An experimental study on the fire resistance behaviour of asymmetric slimfloor beam according to cross section shape variation. Journal of Korean Institute of Fire Science & Engineering, 26(1), 23–30. http://dx.doi. org/10.7731/KIFSE.2012.26.1.023  Kim, K. S., & Lee, D. H. (2011). Flexural behavior of prestressed composite beams with corrugated web: Part II experiments and verification. Composites Part B: Engineering, 42(6), 1617–1629. http://dx.doi.org/10.1016/j.compositesb. 2011.04.019  Kim, K. S., Lee, D. H., Choi, S. M., Choi, Y. H., & Jung, S. H. (2011). Flexural behavior of prestressed composite beams with corrugated web: Part I development and analysis. Composites Part B: Engineering, 42(6), 1603–1616. http://dx. doi.org/10.1016/j.compositesb.2011.04.020  Oh, J.-Y., Lee, D. H., & Kim, K. S. (2012). Accordion effect in prestressed steel beams with corrugated webs. Thin-Walled Structures, 57, 49–61. http://dx. doi.org/10.1016/j.tws.2012.04.005   

Experimental Study on the Fire Resistance Performance of Prestressed Composite Beam with Corrugated Web under Standard Fire with Loading Condition

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