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Every building consists of a load bearing frame, usually created by reinforced con-crete, or by steel, or by the combination of both areas with usual earthquake activity. Although the load bearing frame is not visible after the completion of the construc
251.3 Frame loadings The frame of a building is designed to constantly cope with all gravitational loads (self weight, walls, floors, cars, furniture, humans etc). It should also be capable to periodically cope with loads such as wind pressure and snow and even take into account possible thermal effects. In every building such as the above, there are constant (dead) and moving (live) loads which are imposed upon the frame. Live loads are usually smaller than dead loads, e.g. 3 people and all furniture of the sitting room weight less than 1cm2 of a slab whistle a car weights almost the same as only one beam. Abstracts from the book of Apostolos Constandinides titled ‘Earthquake resistant buildings’, Vol. A, chapter 1.3 published in low resolution in the site of pi-Systems International S.A. www.pi.gr 26 Apart from coping with usual loadings, in areas with intense earthquake activity the frame should be designed with a surplus of bearing strength distributed in such a way that in the rare but crucial moments of an extreme earthquake to ensure the stability of the building and avoid extensive damages. The most characteristic attribute of an element is its mass. The type of forces imposed upon an element depends on the force field that the element is surrounded from. Earth’s gravitational field creates the force of gravity commonly referred as weight. What is more, during an earthquake there are horizontal accelerations that create the horizontal forces of the earthquake. These forces are imposed upon the building and create the loadings of the frame. These loads can be categorized as gravitational loads, wind loads and earthquake loads. 1.3.1. GRAVITATIONAL LOADS The loads in a building are divided into permanent (dead) and moving (live) loads. The dead loads consist of the self weight of the reinforced concrete structural elements, the weight of walls and the weight of all coverings and coatings. As live loads we consider all loads from humans, furniture, vehicles etc. Abstracts from the book of Apostolos Constandinides titled ‘Earthquake resistant buildings’, Vol. A, chapter 1.3 published in low resolution in the site of pi-Systems International S.A. www.pi.gr 27Dead Loads The density and corresponding specific weight of the materials used in construction are as follows: Reinforced concrete ρ=2.50t/m3 (ε=25.0 kN/ m3) Lightweight regulating concrete ρ=0.80t/m3 (ε=8.0 kN/m3) Sand mixture ρ=2.00t/m3 (ε=20.0 kN/m3) Marble ρ=2.70t/m3 (ε=27.0 kN/m3) The total dead loads of one m2 for the slab in the above picture is g=0.15*2.50+0.04*0.8+0.02*2.0+0.02*2.7=0.5t. Summarizing, the self weight of one cm2 of an ordinary slab is 0.5t (weight 5.0 kN) Abstracts from the book of Apostolos Constandinides titled ‘Earthquake resistant buildings’, Vol. A, chapter 1.3 published in low resolution in the site of pi-Systems International S.A. www.pi.gr 28 Water ρ=1.00t/m3 (ε=10.0 kN/m3) The dead load of one m2 of a slab in a swimming pool filled with 1m of water is 1.4t (weight 14.0 kN) Land soil ρ=1.70t/m3 (ε=17.0 kN/m3) The dead load of one m2 of a slab in a garden filled with 1m of soil is 2.1t (weight 21.0 kN) Abstracts from the book of Apostolos Constandinides titled ‘Earthquake resistant buildings’, Vol. A, chapter 1.3 published in low resolution in the site of pi-Systems International S.A. www.pi.gr 29 Abstracts from the book of Apostolos Constandinides titled ‘Earthquake resistant buildings’, Vol. A, chapter 1.3 published in low resolution in the site of pi-Systems International S.A. www.pi.gr 30 Single wall ρ=0.21t/ m2 (ε=2.1 kN/m2) Double wall ρ=0.36t/ m2 (ε=3.6 kN/m2) A wall with 1.0m length, 2.85m height and 10cm width has a mass of 0.6t (weight 6.0 kN) Live loads Loads from people: Regular load of humans ρ=0.20t/m2 (ε=2.0 kN/m2) Abstracts from the book of Apostolos Constandinides titled ‘Earthquake resistant buildings’, Vol. A, chapter 1.3 published in low resolution in the site of pi-Systems International S.A. www.pi.gr 31The live load of one m2 of a house is 0.2t (weight 2.0 kN) Overcrowding ρ=0.50t/m2 (ε=5.0 kN/m2) The live load of one m2 of a public building is 0.5t (weight 5.0 kN) Loads from cars ρ=0.25t/m2 (ε=2.5 kN/m2) The distributed live load of one m2 of a parking space is 0.25t (weight 2.5 kN) Abstracts from the book of Apostolos Constandinides titled ‘Earthquake resistant buildings’, Vol. A, chapter 1.3 published in low resolution in the site of pi-Systems International S.A. www.pi.gr 32 The loads from snow are usually smaller from the live loads of people and it varies between 0.6 and 1.5kN/m2. In order to assume an approximate value of the total loads imposed on a building we can calculate 1 m2 of a slab (1m x 1m) In 1m2 of floor, the permanent (dead) loads are 0.5t (weight 5.0kN) and the moving (live) loads are 0.2t (weight 2.0kN). However if we also include in the calculation the loads imposed by beams, columns, walls and coverings, the total dead loads (self weight of the structure) are more than 10kN/m2, whistle the live loads remain unchanged ( 2kN/m2). What is more, in a certain time period during the total life span of the building, the possible extensive permanent loads will reach 100% of the predicted, whistle the total extensive live loads will not go over 30% of the predicted. Therefore, it is obvious that the dead loads are much more than the calculated live loads. This is a major drawback of reinforced concrete structures since there are excessive dead loads required in order to support significantly smaller live loads The maximum live loads of a house are approximately 20% in proportion to the dead loads. Abstracts from the book of Apostolos Constandinides titled ‘Earthquake resistant buildings’, Vol. A, chapter 1.3 published in low resolution in the site of pi-Systems International S.A. www.pi.gr 33 In a random time instance, e.g during an earthquake, the extensive live loads are approximately 6% in proportion to the dead loads. Abstracts from the book of Apostolos Constandinides titled ‘Earthquake resistant buildings’, Vol. A, chapter 1.3 published in low resolution in the site of pi-Systems International S.A. www.pi.gr 34 1.3.2. SEISMIC LOADS The determination of the influence of an earthquake upon a building is always performed by taking into account that the supposed earthquake will impose a horizontal ground acceleration of A = a * g. The Greek earthquake region is divided into 3 seismic zones I,II,III. Each of the zones is assigned a different value of the ‘a’ coefficient: For zone I the coefficient is 0.16, for zone II is 0.24 and for zone III the coefficient is 0.36. A mass M gives a gravitational force of W. At the moment of the earthquake, there is also a horizontal seismic force H, which is calculated as a percentage of the W force. This percentage usually varies between 0.0 and 0.5. However, during intense earthquakes, it can go over the value of 1. The value of ε is directly proportional to the value of the coefficient ‘a’, of the horizontal seismic acceleration. It is also influenced by factors such as the type of soil, the geometry of the frame and the mass concentration in the building. In general, the shape of the distribution diagram of seismic accelerations resembles. a triangular distribution. Abstracts from the book of Apostolos Constandinides titled ‘Earthquake resistant buildings’, Vol. A, chapter 1.3 published in low resolution in the site of pi-Systems International S.A. www.pi.gr [...]... ‘Earthquake resistant buildings’, Vol. A, chapter 1.3 published in low resolution in the site of pi-Systems International S.A. www.pi.gr 29 Abstracts from the book of Apostolos Constandinides titled ‘Earthquake resistant buildings’, Vol. A, chapter 1.3 published in low resolution in the site of pi-Systems International S.A. www.pi.gr 35 The triangular distribution of seismic accelerations.... the same as only one beam. Abstracts from the book of Apostolos Constandinides titled ‘Earthquake resistant buildings’, Vol. A, chapter 1.3 published in low resolution in the site of pi-Systems International S.A. www.pi.gr 30 Single wall ρ=0.21t/ m 2 (ε=2.1 kN/m 2 ) Double wall ρ=0.36t/ m 2 (ε=3.6 kN/m 2 ) A wall with 1.0m length, 2.85m height and 10cm width has a mass... of the total height of the building. Abstracts from the book of Apostolos Constandinides titled ‘Earthquake resistant buildings’, Vol. A, chapter 1.3 published in low resolution in the site of pi-Systems International S.A. www.pi.gr . buildings’, Vol. A, chapter 1.3 published in low resolution in the site of pi-Systems International S.A. www.pi.gr 26 Apart from coping with usual loadings,. buildings’, Vol. A, chapter 1.3 published in low resolution in the site of pi-Systems International S.A. www.pi.gr 27Dead Loads The density and corresponding