STUDY OF EARTHQUAKE RESISTANT BEHAVIOR IN PREFABRICATED...

11th International Symposium on Ferrocement and Textile Reinforced Concrete 3rd ICTRC

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STUDY OF EARTHQUAKE RESISTANT BEHAVIOR IN PREFABRICATED FERROCEMENT OF DEPOSIT. CALCULATION OF MATERIALS.

Henry Hernández Sotomayor1, Hugo R. Wainshtok Rivas2, 1Instituto de Investigaciones Porcinas (IIP), carretera Guatao Km 1 ½, Punta Brava, La Lisa, La Habana, Cuba, 2Instituto Superior Politécnico José Antonio Echeverría (CUJAE), [email protected], [email protected]

Abstract: The paper presents the study of the earthquake-resistance of a precast ferroce-ment Olympic pool. The structural behavior is analyzed under various loading conditions that can act in such a structure. In order to determine the lateral terrain pressure the Ran-kine method is applied, because the friction between the wall and the soil is neglected. Having assessed the state of the acting forces, the design is made for the worst case, after-wards cracking and bending are checked, and the parameters of Specific Surface Rein-forcement(Sr), which is between (0.5cm-1 -3cm-1) and Reinforcement Volume Factor(Vf), ranging from 1% to8%, conditions that must be met by ferrocement structures. After the pool was designed, the amount of material to be used was calculated, and then compared with the reinforced concrete Olympic pool built in Boyaca, Colombia, for the Pan Ameri-can games in 2006 taking into consideration only the material cost.

INTRODUCTION

Within the entire set of problems in the economy constructions, play an important troll e, as they are one of the main branches in the development of a country. They guarantee the growth rates of national GDP, creating new productive capacities in all branches of the economy and the expansion of capacity inn on productive areas, as well as in the im-provement of working conditions and the life of the population. Currently, among all building materials most used is concrete, both precast and cast in situ, as it meets the basic requirements for industrial and civil construction in general The gen-eral trend in the use of reinforced concrete consists in the development of an active and deep work to improve their technical-economic indicators, as well as the creation and im-plementation of, new structural elements which are lighter, cheaper, and all on higher per-centage of industrial production, and have intrinsic better safety and durability. The solu-tion of these tasks is in perfect correspondence with the introduction in everyday practice of construction, the use of thin-walled structures built with ferrocement. Historically ferrocement was invented first than reinforced concrete, and today they differ mainly in the scale. One of them utilizes bigger diameter reinforced steel rods, and coarse aggregates to form the matrix, as is the case of reinforced concrete ,while ferrocement uses fine aggregates and wire, in this case in meshes either waved or welded, Theoretical and experiment all investigations related to ferrocement as a building material, experiences in the design and construction of structures of this material for many different types of industrial and social buildings, ships, tanks, bridges, swimming pools, etc., and the


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years in the and utilization of ferrocement in many countries, confirm the great economic advantage of using ferrocement structures and the aright record of safety, reliability and durability. This papery a about the design of a pool of ferrocement, a very convenient material, as its essentially advantageous in spatial structures of thin walls, where the stiffness and strength are developed through form, having the advantage of being malleable and built in one piece.

ADVANTAGES AND DISADVANTAGES TO SEISMIC ACTIONS

Advantages • Structures with high internal damping. • Adequate control horizontal deformation • Structures with a large reserve of energy that allow for structural recovery even af-

ter being subjected to severe actions. Also, very easy to repair frequently • They are generally low period’s structures with little influence of the side effects P

-Δ. • Their low vibration period allows structures make them affect only slightly emo-

tional behavior of individuals. • While the specific gravity of ferrocement is similar to that of concrete, it stops be-

ing critical of a suitable dimensioning of its elements with small thicknesses • Its tensile string this higher than that of reinforced concrete

Disadvantages • Concentration of armor at the junctions tending to have low resistance of the mor-

tar • Structures in which it is difficult to achieve high levels of ductility are obtained • Unreliable mathematical modeling. For elastic-plastic seismic analysis of a real

building • There is a need for earthquake-resistant belts at floor leveling order to provide ade-

quate strength and rigidity to the floors and roofs of buildings • To guarantee mechanically that the panels forming the vertical eardrums can work

together in building sunder lateral actions of consideration, primarily when the building as more than two levels, bolting between panels is required.

• The study subject pool will have the following general characteristics: Conceived to beburiedwith50m long, 25mwide and a maximum height of 2.5mlocatedin the cen-ter (see Figure 1).For proper water drainage will possess a slope of 2%, this leads to the ends where lanes are located to have2m of height.


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Figure 1: Pool 3D View

The vessel walls are formed with prefabricated ferrocement panels of a 2m length, 1m width and 3.5cm thickness, In order to achieve an adequate stiffness in the working plane, counterforts will be fitted having the same thickness and length shall with a height 2m.

The vessel walls are formed with prefabricated panel’s ferrocement length 2m a 1m wide and 3.5cm thick; to achieve adequate stiffness in the working plane buttresses that have the same thickness and length shall be fitted with a height 2m.

The wall panel’s width was set also 1m in order to match the mesh as they usually come in rolls 1.10m wide. To prefabrication the counterfort the same mold as for the wall will be used, two counter forts can be built with one mold, which is why the thickness of the coun-terfort was taken equal to that of the wall and the width was set as 50cm. . Because both the walls and buttresses are 2m high, the space left to reach the bottom, which varies from 0 at the ends up to 50cm in the center, will be covered by the bottom slab, which will be shaped properly in that area.

The pool was designed for seismic loads. A well-graded gravel, (pure frictional soil) was used as fill material with the following characteristics: volumetric weight (γf) of 22 kN/m3, internal friction angle (Φ) of 35 ° and without cohesion (c =0).

All the structural analysis of this work was performed using the Software, "Autodesk Ro-bot Structural Analysis Professional 2010". After obtaining the solicitation loads, the de-signed was carried out using the method ultimate limit states ULS), in which the loads are overestimated and decrease the resistance capacity of the material considered lesser, thus obtaining the amount of mesh fabrics required for positive and negative reinforcement. It was double checked by means of the Method of Allowable Stresses and volume factor, specific surface area, arrow and cracking of the ferrocement.

For the bottom slab design as hypothesis of was assumed that the level of maximum rise of the water table is at least50cmbelow the bottom of the pool, so the bottom slab works alone as an impermeable layer, since water pressure is compensated by the soil reaction, is there is a balance of forces that ensures that the bottom slab will not been forced.


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DETERMINATION OF RESTING PRESSURE RANKINE

To calculate the upward thrust of the land the Rankine method was applied since it is as-sumed that there is not friction between the floor and the wall. It is considered that the side walk surrounding the pool around its perimeter serves as bracing for the wall at its upper limit and therefore the pressure transmitted by the ground will be static and that the wall will not move. For earthquake-resistant design is necessary to take in to account the dynamic in crease caused by the earth quake, both in field thrust and hydrostatic pressure. In calculating the dynamic earth pressure increase, the book Analysis and design of reinforced concrete re-taining walls, for which the Standard Venezolana 1753-2006, which is very clear topic, was consulted. In the case of dynamic increase of hydrostatic pressure 350.3-01 the ACI which is focused to the study of earthquake-resistant design for a concrete tank was con-sulted. Once obtained the dynamic load in gin creases, the following load combinations were employed: the first combination will consider the time when the water mass ap-proaches the wall (U1*) and the second time simulates the water mass tends to go away from the wall (U2*).U1*=1.2 (PH) +1.4 (IDph)-0.9 (ET) U2*=1.6 (ET) +1.4 (IDet) - (PH) +1.4 (IDph)

Where: HP: Hydrostatic pressure. TT: Terrain thrust. DIhp: Dynamic increase of the hydrostatic pressure. DItt: Dynamic increase of the terrain thrust.

Determination of the dynamic increase of thrust field (IDET)

The effects of earthquake the resting pressure on the structure. According to the Venezue-lan standard, a trapezoidal pressure diagram can adopted, whose heights are: at the upper end of the wall(σxs) and base wall (σxi). 8 (See figure 2).

Figure 2: Increment dynamic of repose push

σxs = 1,5 A0 γ H, Tension in the pool´s upper part σxi = 0,5 A0 γ H, Tension in the pool´s lower part


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Where:

A0: The ground acceleration as the zoning map. In this case we take A0 = 0.3 which is the largest value that exists in Cuba and corresponds to zone 3 in Santiago de Cuba.

γ : The specific weight of the filling material that generates thrust in rest (= 22 kN / m3).

H: is the wall height (H = 2m).

In the diagram in figure 2.12 is shown how to plot and calculate the resulting pressure and also indicates that is concentrated to 0.6 M, but in this case modeling will be performed with a more realistic pressure distribution.

Determination of the dynamic increase in hydrostatic pressure (IDHP) The dynamic increase of hydrostatic pressure (IDHP) depends on four key components: pressure due to the impulsive side force (Piy), the pressure due to the convertiva lateral force (Pcy), the lateral pressure due to the inertia of the wall (Pwy), and the pressure due to the effect of vertical acceleration (PVY) 0.7

Cálculo de la fuerza lateral impulsiva (Piy)

: Liquid design depth (m).

: Altura height Piy as measured from the Wall base (m).

For deposits with L/h_l≥1,333, hi is calculated by the following expression: H_i/h_l=0.375 Where L is the length of the tank inside in the direction parallel to the force of the earth-quake, or in our case either L or L=25m=50mby dividing by HL= 2mwill always give morethan1,333. Y:It's the distance from the base of the wall to the point at which you want to calculate Piy, in this case the function y =0 and y =HL be evaluated so that the two ex-treme values of the trapezoidal pressures diagram are obtained of Piy. Pi: Total impulsive side force (kN)

P i=ZSIC _i (w_i /R_Wi)

Z: seismic zone factor. Z=0.3for Zone 3which is the largest that exists in Cuba (see Figure 3). S: coefficient depending on the soil characteristics. As in this case soil characteristics are not known as it is intended that the pool is constructible anywhere and as directed by the norm is as summed S= 1.5(see Figure 4).

I: Factor of importance. Because it is intended that the pool can still be used after the quake took I =1.25 (see Figure 5).

RW: response modification factor. RW= 4 because the pool is buried and fixed on the base (see Figure 6).


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Figure 3: Table 4a from ACI 350.3-01 Figure 4: Table 4b from ACI 350.3-01 to determine S.to

determine Z.

Figure 5: Table 4c of ACI 350.3-01for determiner I.

Figure 6: Table 4d of ACI 350.3-01 for determiner Rw.


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Wi: Impulsive component of WL (kN).

WL: Total liquid mass born by the wall (kN).

Note: Whenever it is necessary to determine anything that is a function of L, this will be carried out using 2 methods and the one that yields a worst condition will be adopted, for L=25m and L=50m, as the earthquake can occur in any of the 2 directions.

: Water Specific Gravity (kN/m3).

VL: Water Volume born by the wall (m3).

B: Wall width. B=1m.

Ci: Spectral amplification Factor caused by horizontal movements of the impulsive com-ponent Depends directly of Ti.

Ti: Tank fundamental oscillation period (s).

requency (rad/s).

: Mass (kNs2/m4).

: Mass impulsive component (kNs2/m4).

: Relative mass to the water density (kNs2/m4).

: Gravity acceleration =9,807m/s2.

The value of is the same for L=25m as to L=50m, as the ratio L/WL is the same

Mass per wall width unit (kNs2/m4).


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: Wall height (m).

: Wall thickness (mm).

: Masss relative to the wall material density (kNs2/m4).

: Specific gravity of the Wall material (kN/m3).

: Stiffness to bending perwal width unit (kPa).

For open based-fixed deposits as the case .

EC: Elasticity Module for the wall material (MPa). EC=23500MPa

: Wall gravity center (m).

For deposits having , the spectral amplification factor (Ci) can be calculated by:

Lateral convertive force calculation (Pcy)

: Centroide of Pcy height measured from the wall base(m).

PC: Convertive lateral Force (kN).

WC: Convertive component of WL (kN).

: Spectral amplification Factor caused by the horizontal movement of the convertive

component. Depends directly on TC.

TC: Natural period of the first impact mode (convertive) (s).


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: Oscillation Frequency of the convertive mode (rad/s).

For deposits having , Spectral amplification (CC) can be figured out by means of:

The value is calculated with value, assuming that the quake will act in a direction to the 25m side, where the values are higher and thus preventing the worst case scenario.

Calculo de la fuerza de inercia lateral de la pared (Pwy)

: Effective mass coefficiente .

Note: is an uniformly distributed pressure and its value is not a function of y.

Note: , y are vertically distributed pressures per length unit, in order to distribute them horizontally they shall be divided by the wall thickness, (B=1m), their value stays the same but the units will be kN/m2.

Cálculo de la fuerza por el efecto de aceleración vertical (Pvy)

: Effective Spectral Acceleration of an inelastic vertical response spectrum.

: Spectral amplification Factor caused by the vertical movement .For rectangular depos-

its as our case .

: Vertical / horizontal acceleration ratio. When unknown it is recommended, .

: Unitary hydrostatic pressure as y function.


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Dynamic hydrostatic pressure increase calculation (DHPI)

Structural Design under seismic actions.

After determining the acting stresses in the wall of the pool and on the counterfort, the de-sign is performed by the method of ELU, fissuration, deformation, specific volume sur-face, volume reinforcement factor, are checked and the actinging tension is compared to the permissible. Once finished designing the amount of materials used is determined and subsequently compared with a similar reinforced concrete swimming pool.

MAIN ECUATIONS USED

.) , MPa 5n bigger tha (noTension Acting WM

ft =σ…………………...…1

( )kkhbbRMu 4,012*/8,0 −⋅⋅⋅= , Moment, Equation MELU……… ….……2

SmEm

mWσ

ϕη 1= , Crack width (no bigger than 0.050 mm)………………....3

8%)- (1% .Factor Volumen ,infVcompound

orcementVrerV =

… …………………. 4

)1-2cm - 1-cm (0,5 surface. Specific ,Vcompound

entreinforcem alAsuperficir =S

….. 5


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Table 3: Material costs for the ferrocement swimming pool.

Element Mortar Volume (m3) Reinforcement Weight (T)

Counterforts 5,39 0,51

Wall Panels 10,50 2,01

Bottom slab 31,88 3,92

Total 47,77 6,44

QUANTITATIVE COMPARISON BETWEEN THE OLYMPIC POOL OF BOYACÁ AND DESIGNED FERROCEMENT.

The comparison is done by elements, as follows: Counterforts ferro vs reinforced concrete columns, ferrocement panels that make up the wall vs reinforced concrete panels that make up the wall, bottom slab ferro vs bottom slab reinforced concrete and finally a comparison between the totals. (See graphic 1 and 2).

Figure 7: Comparison based on mortar volume.


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Figure 8: Comparison based on reinforcement weight.

As shown the savings in the amount of materials is considerable, about nine times the amount of mortar and eight times the amount of reinforcement steel.

CONCLUSIONS

After having completed this research has reached the following conclusions:

1. A seismic-resistant design is achieved in the Olympic pool ferrocement which meets all the required d parameters.

2. The amount of materials to be used is 8.5 times less compared to reinforced concrete. Whereas the mesh fabric is more expensive than steel reinforcement of reinforced concrete in Cuba as it is an imported item, the cost savings will ultimately be between 5 and 6 times.

LITERATURE 1. http://upcommons.upc.edu/pfc/bitstream/2099.1/3333/5/34063-5.pdf.

http://www.sitioferrocemento.com/pagina0003.php. 2. Colectivo de Autores, Fundamentos para la aplicación del ferrocemento. Lima, 2000. 3. http://www.mioruro.com/libros/arquitectura/el%20ferrocemento.doc. 4. http://www.araosguzman.org/2011/06/el-ferrocemento.html. 5. http://el-mag.biofutur.org/2010/09/el-ferrocemento/. 6. http://universidaddelmedioambientesurco.blogspot.com/2009/05/estructuras-de-ferro-cemento-

para.html. 7. http://www.ftc.uni.edu.ni/dc/FOLLETOS/Ferrocemento/1_introduccion.ppt. 8. Dr. Ing. Hugo Wainshtok, Ferrocemento. Diseño y construcción. Riobamba-Ecuador 2010 4ta

Edición. 9. http://www.wordreference.com/definicion/alberca. 10. http://www.definicionabc.com/general/piscina.php. 11. http://www.arquigrafico.com/las-piscinas-definicion-partes. 12. http://www.canalconstruccion.comferrocemento.com. 13. Artículo: Guía de Construcción para Estructuras de Ferrocemento, publicado en el 2003. 14. http://www.canalconstruccion.comferrocemento.com. 15. Wainshtok Rivas. Hugo R, Artículo: Uso del Ferrocemento en Cuba.


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16. Rafael Angel Torres Belandria, Análisis y Diseño de Muros de Contención de Concreto Armado. 17. Colectivo de Autores, Seismic Design of Liquid-Containing Concrete Structures (ACI 350.3-01) and

Commentary (350.3R-01). 18. Colectivo de Autores, Guide for the Design, Construction,and Repair of Ferrocement. ACI 549. 19. Braja M. Das. Principio de Ingeniería de Cimentaciones. 1999.A. E. Naaman, Evolution in Ferroce-

ment and Thin Reinforced Cementitious Composites. USA 2009.

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