Analysis of a RCC entrance gate Arch

[D.Jaya]

Dear Structural Engineers

It is required to design a RCC structure as the entrance gate for a land development scheme
I want to start the analysis using a software package and want to model the structure
It is required to clarify the following matters

1) If I model the structure as mentioned and include the loadings,end conditions etc and run the analysis and as a part of the design provide reinforcement according to the resulting Bending moments and Forces is it OK ?Or otherwise do I need to carryout an arch nalysis(by considering this structure as a fixed arch?

2) Since the loading to the structure is small (only the self weight of concrete applies) and also in order to reduce the thrust acting on the abutment/supporting columns if I limit the thickness of the vertical downward projections(of the arch) and the horizontal portion as 3”(75mm) is it ok ?
3) If I limit the thickness to 3” (75 mm), is it possible to use single layer of reinforcement?

 

[WARose]

1) If I model the structure as mentioned and include the loadings,end conditions etc and run the analysis and as a part of the design provide reinforcement according to the resulting Bending moments and Forces is it OK ?Or otherwise do I need to carryout an arch nalysis(by considering this structure as a fixed arch?

You'd probably have to model what it is connecting to.....so you capture the rotational stiffness at that location. You'd also have to consider buckling strength. (In-plane and out-of-plane.) There have been a number of threads here on that subject over the years (with recommended resources).

2) Since the loading to the structure is small (only the self weight of concrete applies) and also in order to reduce the thrust acting on the abutment/supporting columns if I limit the thickness of the vertical downward projections(of the arch) and the horizontal portion as 3”(75mm) is it ok ?
3) If I limit the thickness to 3” (75 mm), is it possible to use single layer of reinforcement?

Seems pretty tight to me. I don't know what code you are under, but under ACI 318, this isn't enough cover for something exposed to weather. (Assuming the bar is as the center of the 3" thickness.)

 

[D.Jaya]

Dear WARose (Structural)
Thanks for your valuable comments

 

[HTURKAK]

You may prefer precast arch beam ..in this case , you may model with pin connected to abutment columns.
The thickness 75 mm is not reasonable for outdoor conditions. Better you provide 150 mm thk. with still single layer reinf. Provide minimum reinf. and check for accidental loading.

( such a beam should resist accidental point loading of 5.0 tons and the abutments for car crash etc..)

 

[BigH]

RCC = Roller Compacted Concrete???

 

[BAretired]

RCC = Roller Compacted Concrete???

That is also true, plus thirty or forty other definitions. Don't you love acronyms? It seems that some folks believe that RCC means Reinforced Cement Concrete. Seems a bit redundant to me...is there another kind of concrete? But it seems to be in use in many parts of the world, so I guess we are stuck with it.

BA

 

[BAretired]

Why not analyze the gate structure using a frame analysis? The arch portion can be represented by, say four, six or more straight line chords. I think four is probably enough.

One thing to remember is that the bottom steel will have a tendency to pull out of the concrete, because of its curve, so the bars need to be held in place by stirrups anchored properly at the top of the arch.

BA

 

[HTURKAK]

Another kind of concrete is asphalt concrete and can be 4 types depending on the aggregate : macadam asphalt concrete, slag asphalt concrete ,gravel asphalt concrete, sandy asphalt concrete ...