Kišiček Tomislav, Renić Tvrtko, Hafner Ivan, Stepinac Mislav
Faculty of Civil Engineering, University of Zagreb, 10000 Zagreb, Croatia.
Polymers (Basel). 2022 Jun 20;14(12):2513. doi: 10.3390/polym14122513.
Serviceability limit states are very important in the design of reinforced concrete elements but they are complex to calculate. Simplified serviceability calculations are provided in EN 1992-1-1 (2013) for steel reinforced elements. The crack widths are assumed to be acceptable if the bar diameters or bar spacings are not too large, while deflections are acceptable if the slenderness is not too large. In recent decades, FRP bars have become an adequate replacement for steel bars, especially in aggressive environments. The calculation procedures for FRP-reinforced concrete elements (FRPRC) were developed from calculation methods for steel reinforced elements. The first part of this paper demonstrates the procedures and parametric investigation for calculating the maximum bar diameter and bar spacing for the purpose of controlling the crack width, focusing on calculations for the maximum bar diameter for which cracks widths are acceptable. The second part of the paper demonstrates the procedures and parametric calculations for the slenderness limits for concrete elements reinforced with FRP bars in order to satisfy the usual deflection limits. Due to the different modulus of elasticity values of FRP and steel, the tables used for steel cannot be used for concrete beams reinforced with FRP bars. Therefore, new tables and diagrams are proposed in the paper. The new tables and diagrams for the maximum allowable bar diameters for the different modulus of elasticity values of FRP can be useful for the rapid control of the crack width in FRPRC elements. They are conservative compared to the exact calculations because some assumptions taken in the calculations are different to those taken in the exact calculation procedure for the crack width. The results of parametric calculations for the slenderness limits for FRPRC elements are provided in the form of a diagram for different concrete classes. Satisfying the slenderness from these curves will result in a smaller deflection than that allowed for each parameter related to that class of concrete.
正常使用极限状态在钢筋混凝土构件设计中非常重要，但计算起来很复杂。EN 1992-1-1（2013）为钢筋构件提供了简化的正常使用计算方法。如果钢筋直径或间距不过大，则假定裂缝宽度是可接受的；而如果长细比不过大，则挠度是可接受的。近几十年来，纤维增强塑料（FRP）筋已成为钢筋的合适替代品，尤其是在侵蚀性环境中。FRP筋增强混凝土构件（FRPRC）的计算程序是从钢筋构件的计算方法发展而来的。本文第一部分展示了为控制裂缝宽度而计算最大钢筋直径和间距的程序及参数研究，重点是计算裂缝宽度可接受的最大钢筋直径。本文第二部分展示了FRP筋增强混凝土构件长细比限值的程序及参数计算，以满足通常的挠度限值。由于FRP和钢材的弹性模量值不同，用于钢材的表格不能用于FRP筋增强混凝土梁。因此，本文提出了新的表格和图表。针对不同FRP弹性模量值的最大允许钢筋直径的新表格和图表，可用于快速控制FRPRC构件中的裂缝宽度。与精确计算相比，它们是保守的，因为计算中采用的一些假设与裂缝宽度精确计算程序中的假设不同。FRPRC构件长细比限值的参数计算结果以不同混凝土等级的图表形式给出。从这些曲线满足长细比要求将导致挠度小于与该混凝土等级相关的每个参数所允许的挠度。
