​

The saddle-shaped shells, or hyperbolic paraboloids, often joined together to form a 

pitched roof or an inverted umbrella, were used by many pioneers in structural architecture, 

such as Félix Candela, which introduced a very innovative use of reinforced concrete in thin 

layers or together with some reticulated ribs. 

An innovative semi-prefabricated building system was developed in Italy in the years ’30 of 

XX  cent  by  a  very  active  brick  factory  near  Piacenza,  RDB:  the  SAP  system,  that    allowed building  curved  surfaces  by  prefabricating  light  elements.  After  WW2,  this  technique  was applied also for the new structures covering wide spaces for the developing industry or also for public  leisure,  using  prefabricated  panels  of  the  desired  length.  A  particularly  interesting application was the BISAP (double-SAP) panel that could be adapted for building large shells. 

In  Codogno  (LO),  Italy,  the  BISAP  panels  were  employed  to  cover  a  large  sports  hall, 

spanning about 37 × 26 m, without intermediate supports, resting (mainly) on the four corner 

pillars. Border pitch beams sustain at the top two crossed beams that separate (and support) 

the  four  hypar  fields.  On  the  four  sides,  two  rafter  beams  are  connected  by  horizontal 

prestressed tie beams, in order to minimize displacements and assure the preservation  of the 

original shape.  

The first aim of the structural analysis was to assess the static conditions of the roof under 

the service loads assigned by Italian code for SLS, and then to evaluate seismic vulnerability 

at ULS of the whole sports hall, being a public space subjected to particular safety provisions. 

The FE code used (Straus7) allowed a very careful discretization of the orthotropic slab with 

the correct inclination and twist of the ribs, giving a reliable forecast of the  behavior also in 

seismic conditions: the dynamic analysis of the modal shapes gives a satisfactory response of 

the shell, which maintains nearly unchanged his shape during free vibration modes. The seismic 

safety  of  the  structure  can  be  then  increased  by  simply  augmenting  the  stiffness  of  the  four corner supports, where shear action is concentrated,  by adding ribs to the L-shaped sections 

to  form  cross  shaped  ones.  In  this  way  also  the  slenderness  (and  weakness)  of  additional intermediated pillars could be overcome.

​

== Full document ==

<pdf>Media:Draft_Content_925257152p1145.pdf</pdf>

== References ==

​

[1]  Sprague, T.S. ‘Beauty, Versatility, Practicality’: the Rise of Hyperbolic Paraboloids in Post-War  America  (1950-1962).  Construction  History,  vol.  28,  no.  1,  pp.  165–184,  (2013). JSTOR, http://www.jstor.org/stable/43856033.  

​

[2]  Engel, H. Structure Systems. (1968) London: Iliffe books.  

​

[3]  Journal of the International Association for Shell and Spatial Structures n. 163, Special Issue for the Centenary of the Birth of Félix Candela, Vol. 51 (2010) No. 1 March   

​

[4]  Burger, N. and Billington, D.P.: Felix Candela, elegance and endurance: an examination of the  Xochimilco  shell,  Journal  of  the  International  Association  for  Shell  and  Spatial  Structures, Vol. 47 (2006) No. 3 December n. 152, pp. 271-278(8).  

​

[5]  Modica,  M.  and  Santarella,  F.:  Paraboloidi:  un  patrimonio  dimenticato  dell'architettura moderna. Firenze, Edifir (2014).   

​

[6]  Paolini  C.  and  Pugnaletto,  M.:  Reinforced  brick  lightweight  vaults.  TEMA,  vol.  3,  No.  1 (2017).  

​

[7]  IL, Il Laterizio, bollettino tecnico RDB, RDB, Piacenza (1961) n. 70 e 71.  

​

[8]  IL, Il Laterizio, bollettino tecnico RDB, RDB, Piacenza (1976) n. 158-159.  

​

[9]  Zienkiewicz,  O.C.  and  Taylor,  R.L.  The  finite  element  method.  McGraw  Hill,  Vol.  I., (1989), Vol. II, (1991).  

​

[10] Straus7, Theoretical Manual. Sydney Aus.: Strand7 Pty Limited, 2005.  

​

[11] D.M. 17.01.2018 - Norme tecniche per le costruzioni, Supplemento ordinario alla Gazzetta Ufficiale n. 42 del 20 febbraio 2018 - Serie generale (2018).  

​

[12] Circolare  n.7  del  21.01.2019  Istruzioni  per  l’applicazione  dell’Aggiornamento  delle  «Norme tecniche per le costruzioni» di  cui al D.M 17 gennaio 2018.  S.O. alla Gazzetta  Ufficiale n.35 del 11 febbraio 2019 - Serie generale (2019).

​