Design of Reinforced Concrete Solid Slab Bridge

March 4, 2021


In March 2020,  we hosted a webinar, “Case Study: Reinforced Concrete Solid Slab Bridge" by Mak Guo Shao, a bridge engineer with more than 8 years of experience. In this webinar, we will brief on the engineering reasons behind choosing a deck of such type, the characteristics of the deck, Wood-Armer Moment, design optimization, etc.



Key Points


1. The reason why solid slabs are used for this bridge is that it has a short span, tight radius, non-prestressed reinforcement, and great ability to be built to suit irregular shapes. 


2. Midas Civil helps to cover variables of vehicular loading in BS code much easier.


3. When twisting and bending occur concurrently, both shall be accounted for Wood-Armer moment. 


4. The reduction of the moment due to the physical width of the bearing is purely mechanical and is effective both at working and ultimate loads. 




The RC slab bridge in the webinar


The project example in this webinar has a short span(about 15m) and tight radius. Generally, a solid slab deck is more "constructable" and is much heavier in self-weight than other more complex types of deck. When the spans are short, it has advantages in the savings in cost, time, and construction simplicity. 


bridge configuration


Definition of Traffic loads


There are notional lanes along the curved slab and HA & HB vehicle load of BD 37/01 was applied along those lanes. midas Civil helps to cover variables much easier, e.g. the different distances between the 2 inner axles of an HB vehicle, an HB vehicle straddling between 2 lanes, “loaded length” of HA loading.


traffic lanesdimension of HB vehicle


Consideration of Twisting and Bending by Wood-Armer Moment


Wood Armer method allows moment triads from plates (Mx, My, Mxy) to be transformed into simple bending moments in two directions (Wood Armer moments) for reinforcement design of plate elements.


This is important because the twisting moment Mxy can be significant.

Consideration of Twisting and Bending by Wood-Armer Moment



The Wood Armer moments could be obtained at the top and bottom of plates along with both the reinforcement directions. This option could be accessed by clicking on the ‘Wood Armer Moment’ button as highlighted in the image below.


wood armer-1


Consideration of Rounding of Support Moments


On many occasions, the “peak” hogging moment is greater than the sagging moment. “Peak” hogging moment is calculated assuming “stick” support, which is not the exact case.

The load above the support is “counter-acted” by the support reaction R distributed over d (or d + yb tan 35°). Simply-supported mechanism assumed for moment reduction. Reduction is limited to 10 % × peak hogging moment.


Consideration of Rounding of Support Moments


Watch the Full Webinar Here



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About the Author
Mak Guo Shao | Bridge Engineer

Mak has 8 years of experience in bridge engineering. He has extensive experience of designing complex bridges with challenging requirements. To him, the crux is in the superstructure, i.e. the deck.

He has designed two bridges of solid slab deck, and one of them will be shared here.

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