بررسي رفتار خمشي دال هاي مجوف دو طرفه با گوي هاي لهيده و كيج هاي فولادي محصور كننده

INVESTIGATION OF FLEXURAL BEHAVIORS OF BIAXIAL VOIDED SLABS WITH ELLIPSOIDAL BALLS an‎d STEEL CAGES

در كنار مزاياي مختلفي كه دال هاي توپر در ساخت سقف ها ايجاد مي كنند، وزن بالاي آنها موجب ايجاد مشكلاتي مي شود. به منظور كاهش مشكلات اشاره شده، سيستم هاي مختلفي با نام دال مجوف دوطرفه معرفي شده است. در بعضي از سيستم هاي مذكور، از گوي هاي پلاستيكي كروي و لهيده، كه در كيج هاي فلزي محصور شده اند، استفاده شده است، تا بتن غيرموثر حذف شود. به دليل وجود ابهام در عملكرد خمشي سيستم اخير، در پژوهش حاضر، دو نمونه با مقياس واقعي با ابعاد $300times1200times6500$ ميلي متر)طول $times$ عرض $times$ ارتفاع(ساخته شده است، تا ظرفيت خمشي، ترك خوردگي و خيز دال توپر و مجوف با يكديگر مقايسه شود. در نهايت مشخص شد كه مواردي همچون نمودار بار - تغييرمكان، ظرفيت خمشي و مود شكست دو نمونه شبيه يكديگر است و در مقابل، كيج هاي فلزي موجب افزايش ظرفيت نمونه هاي مجوف مي شوند.همچنين ظرفيت خمشي نمونه ي مجوف با استفاده از روابط 141318ACI قابل پيش بيني است.

A wide variety of systems have been introduced so far for the construction of roofs, as one of the most essential structural components of buildings. A conventional roofing system is the solid slab that offers adequate rigidity to distribute gravitational and seismic loads, while it is also relatively resistant against fire. However, its main drawback is its overweight that increases the associated seismic loads. To resolve this problem, modifications were proposed that resulted in different types of biaxial voided slabs. In one such system, spherical and ellipsoidal plastic balls enclosed in steel cages were used to eliminate ineffective concrete. Due to the novelty of the system, however, little was known about the bending behavior of the roof thus constructed. Most of previous studies have been conducted on spherically-shaped voids ignoring ellipsoidal ones. This is while the effect of supporting cages on voids has not been investigated at all. The present study was, therefore, designed and implemented to study the behavior of biaxial voided slabs containing ellipsoidal plastic balls and the effect of supporting cages on bending behavior. To investigate these aspects of the system, two full-scale bending specimens were cast for investigating bending capacity, cracking distribution, and deflection in solid and biaxial voided slabs. Moreover, the effect of cage longitudinal rods was studied on the ultimate capacity of the bending specimens. Finally, the experimental results were then examined by ACI 318-14 recommendations to put forth suggestions for using the ACI 318-14 equations in designing biaxial voided slabs. It was found that while both solid and biaxial voided specimens exhibited almost similar bending behavior and the same failure mode. Also, the bending behavior of biaxial voided specimen was affected by the steel cages used. So, to use the ACI 318-14 equations, if this longitudinal cage bar is considered, the percentage difference between experimental and calculated results reached just one percent.