Phân tích tính toán kết cấu dầm đỡ vách (dầm chuyển) bằng mô hình giàn ảo

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Tác giả: NGỌC THẮNG NGUYỄN

Ngôn ngữ: vie

Ký hiệu phân loại:

Thông tin xuất bản: Tạp chí Xây dựng, 2024

Mô tả vật lý: tr.88

Bộ sưu tập: Metadata

ID: 380305

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In the theory of reinforced concrete beam structural analysis, the retaining wall support beam, also known as the transfer beam, is a type of bending member with relatively large stiffness and cross-sectional area (where the span-to-depth ratio is less than or equal to 2.5 for continuous spans and 2 for single spans). Elastic analysis results have shown that the assumption of a flat cross-section for the beam is not applicable to the transfer beam
there exists a zone with high stress concentration at the bearing location and especially at the bearing face. The vertical deformations caused by shear forces in the transfer beam are much greater than the deformations due to bending, thus playing a significant role in the total deformation. Moreover, transfer beams often exhibit early cracking along the direction of the principal compressive stress, which is perpendicular to the direction of tensile stress. In many cases, cracks appear vertically or diagonally when the beam is subjected to shear-induced damage. The working state of the transfer beam at the ultimate limit state must be calculated using a structural model, known as the "strut and tie" model or "virtual strut" model, which is the most suitable model for reinforced concrete beams with side reinforcement. In this paper, the author analyzes the design calculation content of the transfer beam through specific examples based on the design standards 22TCN 272-01 of the Ministry of Transport of Vietnam and the American standard ACI 318-2002. Keywords: Tensile stress
principal compressive stress
transfer beam
strut and tie Model.Trong lý thuyết tính toán kết cấu dầm bê tông cốt thép, dầm đỡ vách còn được gọi là dầm chuyển là loại cấu kiện chịu uốn có độ cứng và tiết diện hình học tương đối lớn (tỷ lệ chiều dài nhịp trênchiều cao nhỏ hơn hoặc bằng 2.5 đối với nhịp liên tục và 2 đối với nhịp đơn) và trạng thái làm việc của hệ kết cấu từ hệ dầm cột chịu lực sang hệ dầm vách chịu lực. Các kết quả phân tích đàn hồi đã cho thấy những giả thiết tiết diện phẳng cho dầm không thỏa mãn đối với dầm chuyển
tồn tại một vùng chịu ứng suất lớn tại vị trí gối tựa và đặc biệt là ở mặt gối tựa
các biến dạng dọc do lực cắt gây ra trong dẩm chuyển là lớn hơn nhiều so với biến dạng uốn, do đó đóng vai trò nhiều hơn so với tổng biến dạng. Mặt khác dầm chuyển thường có vết nứt xuất hiện khá sớm theo phương của ứng suất nén chính, tức là vuông góc với phương của ứng suất kéo. Trong nhiều trường hợp, khe nứt xuất hiện thẳng đứng hoặc nghiêng khi dầm bị phá hoại do lực cắt. Trạng thái làm việc của dầm chuyển trong giai đoạn giới hạn cực hạn phải được tính theo mô hình toán cơ, là mô hình tốt nhất đối với dầm bê tông cốt thép có bố trí cốt thép sườn dầm, gọi là mô hình “chống và giằng” (Strut and tie model) hay còn gọi là mô hình giàn ảo. Trong bài báo này tác giả phân tích nội dung tính toán thiết kế dầm chuyển qua ví dụ cụ thể dựa trên tiêu chuẩn thiết kế cầu 22TCN 272-01 của Bộ Giao thông vận tải Việt Nam và tiêu chuẩn Hoa Kỳ ACI 318-2002. Từ khóa: Ứng suất kéo
ung suất nén chính
dầm chuyển
mô hình “chống và giằng”.

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