Ceiling structuresCEILBOT-PROJECT

INTRODUCTION TO CEILING STRUCTURES

• History• Situation today• Loading• Fastening• Vibrations and sound• Risks

Eelon Lappalainen

A.Aalto, Maison Carré, France

”A ceiling is an overhead interior surface that bounds ("ceils") the upper limit of a room.” Wikipedia

History• Ceiling is quite new ”invention” in residential

buildings, started to become general after WW II

• Ceilings were used before WW II usually in castle’s and churches

• Before 19th century ceilings were mostly made of timber or masonry

• During 19th century cast iron, steel and concrete were also used in ceilings

– Ceiling made of cast and wrought iron: 1780 - 1900

– Ceilings made of concrete: 1850 -– Ceilings made of steel: 1880 -

• Typical for ceilings is diversity of different structures and support systems

• Old ceilings were designed mainly to support it’s own weight -> adding more load will usually cause problems (big deflection, cracking, even collapse)

• Design methods and quality of materials varies a lot

Benedectine Abbey of Einsiedeln, Switzerland

Situation today• Pre-fab pre-stressed slabs (etc. hollow

core slab) are commonly used• In residential buildings ceiling is

normally in washrooms and hallways (installations are hidden behind ceiling)

• In office buildings ceiling is usually in large areas and hide’s structures and installations (main installation routes are in hallways and vertical shafts)

• Small family houses, day-cares, ware-houses and even some industrial buildings timber structures and ceiling is used

• Fire regulations strongly defines materials what is allowed to use in certain buildings

• Modern ceiling usually hangs from load bearing structure by fasteners

Installations inside the ceiling

Loading• Basic loads are given in design codes

(Eurocode, ACI, DIN, RakMK)• Dead load• Live load (1,5…10kN/m2)• Ceiling load (~0,2…1kN/m2)• Dead load, live load and ceiling loads

for are in horizontal structures mainly vertical loads

• Installations (HVAC, motors, robot etc.) causes three dimensional loads

• Three dimensional loads are usually handled separately in structural dimensioning

• For simple calculations dynamic loading can be expressed:

– static load x dynamic factor– displacements are limited

• Complex dynamic problems are usually calculated by FEM

Fastening• Ceiling is fastened to load

bearing structure (slab, beam, truss)

• Fasteners and anchors should carry mainly vertical dead loads from ceiling and attached equipment (electric, HVAC)

• There are numerous different fastener types

• All fasteners and anchors which are strained dynamically, should be approved for such purpose

• Actions causing fatique will decrease strength

TIMBER

SCREW

HOLLOW CORE SLAB

LOCKING PART

FIXING DEVICE

COLD FORMED STEEL PROFILE

FIXING DEVICE

SCREW

NUT&BOLTANCHOR BOLT OR

CHEMICAL ANCHOR

CONCRETE SLAB

Vibration and sound insulation• Walking 1,6…2,2Hz• Natural frequences are divided in two

classes:– Low frequency floor (f0<8Hz)

• Heavy, long span– High frequency floor (f0>8Hz)

• Light or mid-weight• Resonance should be avoided by

tuning• Passive damping (fixing points)• Active damping (etc. robot equipped

with sensors, regulators and actuators) • Structure-borne (impacts) and airborne

sounds should be avoided • Impact sound level L´n,w<53dB

(residential buildings in Finland)• Sound reduction index (airborne) R

´w>55dB (residential buildings in Finland)

• Robot fixing points and railing systems should be insulated from structure

Free oscillation Free oscillation, damping

Forced oscillation Forced oscillation,

damping

steady-state

steady-state

Vibration sources and isolation

Risks

• Overloading and wrong material choises could be fatal and may cause serious damages and even loss of life’s

• Fixing type must be safe and inspected properly

• All fixings should be designed so that they are easy to check and maintain

• Design boundaries should be clear; who is designing and what -> responsibilities

Collapsed spa ceiling in Kuopio, Finland

Sources• RT 84-10916, Alakatot ja sisäkattoverhoukset• RT 83-10902, Välipohjarakenteita• Betoni Suomessa 1860-1960, Betoniyhdistys ry• Tutkintaselostus B 4/2003 Y, Kylpylän alakaton romahtaminen

Kuopiossa 4.9.2003, Onnettomuustutkintakeskus• Terasrakenneyhdistys.fi//Esdep• wikipedia.org• SFS-EN 1991-1-1• Fastening Technology Manual, Hilti Corporation, 2004• Lattioiden värähtelysuunnittelu, VTT Rakennus- ja

yhdyskuntatekniikka• KSU-3010 Mekaaniset värähtelyt, Luentomoniste, Machine

Dynamics Lab, Tampere University of Technology• Teräsrunkoisten välipohjien värähtelyjen hallinta, VTT

Rakennustekniikka