QUESTION SEVEN

$($a$)$ Explain the effect of max$-$spans $($hollow blocks$)$ on the seismic performance of Rc slabs

$($b$)$ Explain why it is advisable to stagger the max$-$span joints in adjacent rows

$($c$)$ Explain why max$-$span slabs are made solid at about $0\mathrm{.}5$m to $1$m from the support

$($d$)$ Determine the depth of topping to be provided to be provided in a max$-$span $($ribbed hollow

blocks$)$ slab assuming $20$mm cover, $12$mm bars over supports, $6$mm mat $($A $142$ BRC$)$ also to serve as

distribution steel, $10$mm concrete spacers between the A$142$ BRC and the hollow blocks.

$($e$)$ A max$-$span slab continuous over three equal spans of $4$m is supported on walls. It carries a

variable load of $1\mathrm{.}5$ KN $/$ m$^2,$ has a topping of $75$mm$,$ granolithic floor finish of $25$mm$,$ underside

plaster of $25$mm hollow blocks of $300$mm long, $150$mm deep, $380$mm wide at the top, $300$mm wide at the

bottom and weighs $7$kg$.$ The x$-$section of the max$-$span slab is shown in the Figure III. To allow for

the passage of the porker vibrator, the ribs are $70$mm at the top and $150$mm at the bottom. The

materials are grade $30$ concrete and

grade $460$ steel. Assume $20$mm cover, $12$mm diameter bars, unit weight of concrete is $24$

KN $/$ m$^2,$ unit weight of finishes is $20$ KN $/$ m$^2$

$($i$)$ Determine the number of max$-$spans per square meter

$($ii$)$ Determine the ultimate load of the slab in

KN $/$ m$^2$

and per $0\mathrm{.}45$m strip of the slab

$($iii$)$ Using coefficients, draw shear force diagram

$($v$)$ Given that there is one bar of diameter $12$mm per rib, and the tension steel over supports is

specified as T$1201-200$T$1,$ and the slab is made solid at $500$mm from the support, check the shear

resistance of the slab.