Modares Civil Engineering journal
مهندسی عمران مدرس
MCEJ
Engineering & Technology
http://mcej.modares.ac.ir
1
admin
2476-6763
10.22034
fa
jalali
1390
8
1
gregorian
2011
11
1
11
3
online
1
fulltext
fa
مدل رفتاری الیاف فولادی خمیده در بتن
Simple Fiber Poullout Model for Aligned
Hook Eneded Stell Fibre
چکیده- در این پژوهش یک مدل ریاضی چند خطی برای پیش بینی رفتار بیرون کشیدن الیاف خمیده با بدنه صاف از بتن ارائه
شده است. بنای این مدل بر روش نیرویی استوار است. در این مدل ابتدا با استفاده از نظریه رابطه بین "تنش مهاری و لغزش بین
بدنه الیاف و ماتریس کنار آن" و فرض توزیع یکنواخت تنش محیطی، یک مدل ساده ریاضی برای الیاف مستقیم استخراج شده
است؛ و سپس با استفاده از آن، مدل ریاضی الیاف خمیده با تجزیه و تحلیل نیروها در محل های خمیده قلاب ها ارائه شده است .
یکی از ویژگی های این مدل توانایی آن در براورد منحنی نیرو–لغزش الیاف در سه محدوده مهار کامل، جداشدگی نسبی و لغزش
الیاف است. در این مدل امکان پیش بینی سازوکار های اصلی لغزش و میزان نیروهای متناظر ارائه شده است. سرانجام این مدل با
نتایج تحقیقات آزمایشگاهی موجود و همچنین انجام آزمایش بیرون کشیدن الیاف، اعتبار سنجی شده است.
Abstract:
Cement based material such as mortar and concrete are brittle in nature and crack under low tensile
stress and strain levels. Adding discontinuous fibers as reinforced concrete remedy some concern
related to cement based material brittleness and poor resistance to crack growth. After cracking the
fibers arrest between two crack faces and provide mechanisms that abate their unstable propagation [].
Fibers bridging force is achieved by transmission of the bond interfacial stress between the fiber and
surrounding matrix. The resistance of the section to further crack opening depends largely on the fiber
pullout mechanisms and related possibilities including complete fiber pullout or fiber fracture []. The
high levels of interfacial shear strength may prevent fibers from complete debonding and result in
fiber fracture. Although the strength of composite may increase, its toughness reduces significantly
and failure is brittle. On contrary the low interfacial shear strength causes complete fiber debonding
from matrix and fiber pullout. The effectiveness of fiber is often assessed by using single fiber pullout
test. The experiments have shown that in improving the pullout resistance, hook-end fiber is more
effective than straight fiber [, ,].The pullout process of hooked-end fibers is more complex than that of
straight steel fibers and there is one additional deformation mechanism because of mechanical
anchorage. So the analytical models for straight fiber are not valid for the fibers having mechanical
anchorage. The main objective of this paper is to develop an analytical model for hook-end steel fiber
pullout behavior. In this model the concept of bond shear stress versus slip relation between fiber and
matrix has been used to develop fiber force and bond stress. Also the interfacial stress has been
supposed that to be distributed uniformly. Based on two mentioned assumption a theoretical relation
have been developed for aligned straight fiber at first. Then this relation is promoted for hook ended
steel fiber pullout response. In order to do this, the effect of hooks on force and stress distribution has
been analyzed along the fiber length and utilized for developing the pullout response of hook ended
steel fiber. Based on obtained relation, the hooks change the fiber along the fiber length at the hooks
and this force will be decreased with constant coefficient which is the function of fiber geometry.
Despite that a normal force and its frictional force will be occurred at the hook bent. Decreasing the
fiber force and creating a normal force at the hook bend are the factors that create an extra resistance
force against the pullout in hook-end fiber. This study investigates these factors and develops the
relations in order to calculating the maximum load required for pulling out the hook-end fiber. Finally
the model has been validated by experimental results on the hook-end steel fiber. Proposed model is
able to estimate the main pullout mechanism due to mechanical anchorage of hooks.
بتن های الیافی,الیاف خمیده,مهار کامل,جداشدگی نسبی,لغزش
Fiber pullout,Hook-end,bond stress,mechanical anchorage,bearing effect
0
0
http://mcej.modares.ac.ir/browse.php?a_code=A-10-1000-3160&slc_lang=fa&sid=16
P.
Ghoddousi
پرویز
قدوسی
100319475328460042049
100319475328460042049
Yes
R.
Ahmadi
رسول
احمدی
100319475328460042050
100319475328460042050
No
M.
Sharifi
مهدی
شریفی
100319475328460042051
100319475328460042051
No