Design of Pavement Lights

[hemis]

I am having to prepare safe-load and maximum-span tables for a series of reinforced-concrete pavement-lights. I am using BS 8110 for my design but I am also in the process of converting to Eurocode.

My problem is this. I have designed the lights as a series of one-way spanning beams with perfect lateral restraint. When I compare my results with Luxcrete's safe load tables for pavement lights (very kindly supplied by cds72); I do not get the same results: or even near them.

From my calculations, Luxcrete's span ratios for deflection exceed those permitted in BS 8110. Unfortunately, I do not have any case studies or standards to follow to compare my results with.

Has anyone any experience of pavement-light or small single-reinforced beams (Lintels?) that I could share ideas with. At these small depths of beam, do scale effects come into play? Did the authors of BS 8110 consider very small beams? I have not found any mention of small beams in the code.

 

[ishvaaag]

May they be using fiber reinforced concrete in more than steel reinforcement?

 

[hemis]

They make no mention of fibre concrete in the literature.

I am reading a text by Bernard Maidl on the subject at the moment and Maidl has shown that there is an improvement in crack widths (finer and more evenly distributed) but I have not found the amount of improvement yet.

However, when I check the span/depth of a Luxcrete pavement light with ribs of approximately 55mm wide by 110mm deep (giving an effective depth = 70mm with 10mm bar and 25 cover); The SD ratio for a 2950mm span is 42. I am not sure I could justify that ratio, even with fibre reinforcement.

Maybe pavement lights are not subject to BS 8110 SD ratios?

I was given this link by cds72 for Luxcrete span tables

http://www.luxcrete.co.uk/datasheets/LUXCRETE_FLOOR_PAVEMENT_LIGHTS_AND_SMOKE_OUTLET_PANELS.pdf

 

[ishvaaag]

Certainky, that is prestressed concrete range ... top range. May the wires be prestressed? Even then quite curious detail would be required for anchorages of wire, loops, then some 90 deg turn? And kept within the panel, otherwise the cut end effects should show. Anyway could be enough to justify the gain at the central sections and maybe the ones closer to support are not critical for the given loads, or so makes some special "plastic" resilient concrete (high tensile strength).

As well, glass embedments constitute a composite structure with the concrete. Except for the transverse ribs they (as long adherence remains high) must be enhancing overal tensile (and flexural strength). And trhough a complicated transfer of flexural solicitations, then you have the transverse rib to be for flexure a full rectangular section of the overall width, reinforced by the wires ... that the span/depth ratio suggest be prestressed.

 

[csd72]

hemis,

I would expect that the luxcrete values are based on testing rather than code values.

 

[hemis]

Thank you for your responses.

Not sure if Luxcrete prestress.

I telephoned the technical department at Luxcrete and (this is from my memory - no litigation please) the calculations and testing carried out at Westminster University has been lost in a recent management re-organisation. I may consider approaching Westminster to see if the testing is in the public domain.

Am I able to model the pavement lights as a grillage in FEM? I know nearly all the properties of the material. I use PROKON for my modelling.