Eğilme Altındaki Beton Kirişlerin Çatlak-Bant Genişliği Yaklaşımı ile Boyut Etkisinin Analizi

Öz

Bu araştırmada, yarı gevrek malzemelerdeki boyut etkisinin hasar-plastisite modeli kullanılarak çözümlemesi sunulmuştur. Çentikli ve çentiksiz üç noktalı eğilme deneyleri üç boyutlu (3D) sonlu eleman modeli ile analiz edilmiştir. Bu amaçla, Abaqus yazılımı kullanılmıştır. Beton elemanların gerçekçi bir şekilde analizinde, özellikle boyut etkisinin dikkate alınmasında, çatlak bant genişliği yaklaşımı uygulanmış, hasar-plastisite modelinin etkinliği araştırılmıştır. Kırılma mekaniği parametrelerinin bulunması amacıyla, açıklık-yükseklik oranı, L/D=2.176, olan üç noktalı eğilme deneyine ait 2D sonlu eleman modeli, her bir çentik derinliği için oluşturulmuştur. Bu modelde, kiriş 8-düğüm noktalı dörtgen düzlem gerilme elemanları ile modellenmiş ve çatlak uç noktasındaki tekillik “quarter point” tekniği kullanılarak oluşturulmuştur. Bu analizler sonucunda, J-integral bulunmuş ve enerji salınım oranı hesaplanmıştır. Elde edilen sonuçlar literatürde verilmiş olan deney sonuçları ve ayrıca Bazant’ ın boyut etkisi eğrisi ile karşılaştırılmıştır. Bu çalışma, çatlak bant genişliği yaklaşımı uygulanmış hasar-plastisite modelinin, beton gibi malzemelerde, boyut etkisini yakalamak için uygun olduğunu göstermiştir.

Anahtar Kelimeler

• sonlu eleman modeli
• Çatlak analizi
• ağ boyutu bağımsızlığı
• çentik boyu

Size Effect Analysis of Concrete Beams Under Bending Using Crack-Band Approach

Öz

Analysis of size effect phenomenon in quasi-brittle materials is presented in this research using damage plasticity model. Notched and unnotched specimens under three-point bending fracture test are analyzed by setting a 3D finite element model. For this purpose, Abaqus software is utilized. Concrete damage-plasticity model (CDPM) enhanced with crack band approach is used to conduct simulations of concrete specimens. The efficiency of this model is investigated especially for size effect phenomenon. 2D finite element model is setup for three-point bending beams in order to estimate fracture parameters for specific span to depth ratio, L/D=2.176. The simulations are conducted for each different notch depths. 8-node quadratic plane stress elements are used to define 2D domain and singularity field at the notch tip is modeled using quarter point technique. Energy release rate is calculated using J-integral approach. Obtained results are compared to experimental ones reported in literature and are also compared to the Bazant’s size effect law. This study shows that concrete damage-plasticity model enhanced with crack band approach can capture size effect observed in concrete-like materials’ fracture. 

Anahtar Kelimeler

• Size effect
• crack band approach
• mesh size independency
• notch length
• finite element analysis

Kaynakça

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