Dear Bentley team,
I encountered an issue regarding crack width calculation in RCDC with ACI 318M-14 code, described as follows:
Refer to the outputs attached below. The considered beam is B5 and Zone is Top right.
When beam is designed with permissible crack width set as 0.25mm, then actual crack width with 1 layer of bar with 3 no. of 13 dia bars is coming out to be 0.1539mm which is within the limit.
Now for the same design if I restrict the permissible crack width to 0.2mm, then also it should satisfy the design (as 0.1539mm < 0.2mm). But when I reduce the limit to 0.2mm, RCDC is increasing the rebar to 2 no. of layers with 3 no. of 13 dia bars in first layer and 2 no. of 13 dia bars in second layer.
Changing only the permissible crack width limit should not ideally affect the actual crackwidth calculation. But it is somehow dependent on that and leads to increase in rebar. Please help in rectifying the issue.
Please find attached RCDC file, and two output sheets with maximum crack width set as 0.25mm and 0.2mm for your reference
. PDFPDFFMO_P01_01(02.12.2021)-NV-2-Beam-1-0 m.rcdx.7z
HiThe RCDC file attached by you is of 1kb size. Please re-send the RCDC file. Also please mention the RCDC version.
Hi,
Please find attached the requested file. I am using the latest version of RCDC (v11.01.00.180).
Thank you
5706.FMO_P01_01(02.12.2021)-NV-2-Beam-1-0 m.rcdx.7z
Hi,Thanks for sharing RCDC file. We will revert to you at earliest.
Can you please provide an update.
Hiwe have investigate this issue. The Ast required for the Crackwidth should not change if permissible Crackwidth value is changed. following are our findings,We have observed that the number of rebar to be provided in single layer have been changed to 3 for 200mm width beam. By default value was 2.if you maintain the rebar numbers as 2 on this form it will give the same design output when the permissible Crackwidth is 0.25mm and 0.2mm.We have some internal design flow to check whether the Crackwidth is satisfied with highest diameter if it fails for the preferred rebar arrangement and diameter. For 200mm width it has considered 2 rebars for initial checking of Crackwidth with 13 diameter.
When user changes the rebars numbers on above form, in few cases it showing Ast required without optimization. In this case Ast required is changed as for 2 rebars and 13mm diameter initially it failed in Crackwidth if permissible limit is 0.2mm. it passes if the permissible Crackwidth is 0.25mm. When it failed in case of 0.2m, Ast has increased till it satisfied. With this Ast final detailing of the reinforcement is done.We need to improve the internal logic when user provides the more / less number of rebars for given width. We will take this as a defect in RCDC and we will try to resolve in near future.