体外及体内无黏结预应力梁的有限元模拟

为简化无黏结预应力梁的分析过程，利用通用有限元程序建立了体外及体内无黏结预应力混凝土梁
的分析模型.该模型由两类主单元组成，即混凝土梁单元和体外/体内无黏结预应力筋桁架单元这两类主单
元的端部节点用多点约束（MPC）连接.在体外预应力梁的转向块处，或沿体内无黏结预应力梁全跨并以比
较小的间隔处，设置刚度足够大的弹簧单元利用修正的Riks算法跟踪结构的非线性全过程响应.分析结果
表明，二次效应会对体外预应力梁的弯曲刚度和极限承载力产生较大的不利影响，无黏结预应力筋的极限
应力增量随着非预应力筋配筋率的增加而减小.

Finite element simulation of beams prestressed with external or internal unbonded tendons

For simplifying the analytical procedure of unbonded prestressed beams, an analytical model of concrete beams prestressed with external or internal unbonded tendons was proposed by using a general purpose finite element program. The proposed model adapted two types of main element including beam element for concrete and truss element for external or internal unbonded tendon. The end nodes of main elements were connected with multi-point constraints(MPC). Spring elements with very large stiffness were set up at the places of the deviators of externally prestressed beams, or along the span with relatively little space of unbonded internally prestressed beams. The nonlinear full-range structural response was traced by the modified Riks method. Analytical results show that the second-order effect result in inferior influences on the flexural stiffness and the ultimate load-carrying capacity of externally prestressed beams, and that the ultimate stress increment in unbonded tendon decreases with increasing ratio of unprestressed steel.