عملكرد ژيوتكنيكي سيستم راديه‌مركب با ملاحظه‌ي متغيرهاي شمع هاي منفصل

GEOTECHNICAL PERFORMANCE OF PILED RAFT FOUNDATIONS WITH DISCONNECTED PILES AND EFFECTS OF VARIOUS DESIGN FACTORS

استفاده از شمع هاي كاهنده‌ي نشست در طراحي فونداسيون راديه مركب (PRF)، سبب كاهش تعداد و يا ابعاد شمع ها مي‌شود. در اين حالت امكان ايجاد تنش محوري بالا در شمع ها و يا آسيب به اتصالات وجود خواهد داشت. يك گزينه استفاده از سيستم راديه مركب با شمعهاي منفصل است. در اين تحقيق با استفاده از نرم افزار ABAQUS، ضمن مدل سازي سيستم راديه‌مركب مدل فيزيكي، موارد عملي و مطالعه‌ي موردي، به بررسي نشست، تنش تماسي، و تنش محوري شمع پرداخته شده است. در ادامه، تاثير ارتفاع شكاف و چيدمان شمع ها در پلان بررسي و آرايش بهينه معرفي شده است. نتايج نشان مي دهند كه با استفاده از شمع هاي منفصل، نسبت بار شمع ها به كل بار كاهش و صفحه‌ي خنثي به اعماق پايين-تر انتقال مي يابد. همچنين با كاهش ارتفاع شكاف، تنش محوري بيشينه‌ي شمع و نسبت بار شمع به كل بار افزايش، و با تمركز شمع هاي منفصل در مركز راديه، نشست و مجموع تنش شمع ها كاهش مي يابد

In the conventional design of deep foundations, it is usually assumed that the entire design load of the structure is carried by the piles, and the entire system acts as a pile group. Pile groups are conventionally designed by adopting a relatively high factor of safety to the piles, and the major design criterion is the bearing capacity of the group. The piled-raft foundation (PRF) is a recent design concept, which is used as an effective method of foundation design to reduce settlements of structures. Recently, the use of settlement reducer piles in the design of piled raft foundations has led to the reduction in number or dimension of the piles. However, the system may involve high axial stresses to be induced in a relatively small number of piles; or in the occurrence of damage to structural connections. Therefore, an alternative approach is to disconnect the piles from the raft. This system is known as the disconnected or non-connected piled raft foundation (DCPRF or NCPRF). The use of numerical analyses using finite element techniques has become popular in recent years in the field of foundation engineering. Because of rigorous interaction for piled raft foundation elements, physical modeling measurements and case history records have been considered to justify numerical modeling results. Finite element modeling using ABAQUS software, with emphasis on determination of settlement, contact pressure and axial stress of piles, has been carried out. Also, effects of gap height-distance between the raft and the disconnected pile heads, and pile group arrangements, have been examined in order to optimize the design approach. Results indicate that using disconnected piles, the ratio of pile load to total load decrease and the neutral plane (the plane of maximum structural force in piles) shifts to lower depths. Also, reducing gap height leads to an increase in the maximum axial stress of the piles and the pile load to total load ratio. Moreover, concentration of piles at the center of the raft reduces settlement and pile stress.