The Structural Engineer journal in 2011 published 2 technical notes delving into hand calculation methods to analysis the above criteria on simple buildings.
Denis Camilleri outlines the practice as undertaken in the structural design office of DHI Periti in the features:
Rotation of supporting small bearing pads in buildings TSE 89(3) May 2011.
The methods outlined for the calculation of deflections revolve around the method outlined bythe BCSA in producing deflection coefficients C for steel members as obtained from Figure 1.
The required moment of inertia I in cm4 is obtained from I = CwL3.
Now this method may be scaled to be applicable for use in other structural materials such as timber. This scaling is obtained from the quotient of Young's Modulus E for steel divided by E for timber. For timber the C value, thus works out at around 30 times the respective steel value.
Vibration effects in steel or timber are similarly catered for, by adopting the relative higher deflection span ratios than normally adopted for designs based on deflection criteria. It is then noted that it is even easier to go from a deflection span ratio onto a rotation calculation.
The rotation in radians is given by the simple relationship equating to:
3.2 X deflection span ratio.
These hand calculations address the serviceability requirements dwelling on deflection, rotation at supports and vibration characteristics, as dependent on the use of the structure and its effect on the user. It is quite embarrassing to explain to an annoyed user that his cracking pattern is of no structural concern and that he has to learn to live with these cracks.
A sore point in the engineering profession is the undercutting of fees. This should not be addressed by limiting the structural analysis necessary, as repercussions late in the day are costly to resolve. One of the ways to address this is by streamlining engineering solutions making their use more time efficient. This is what the notes address.
Denis Camilleri, CEng FICE, ICE Member in Malta