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Genetic Analysis of Concrete Crack in Hydroelectric
Station’s Plant Based on FEM
Huang Shu-ping 1,a , Peng Xuan-mao 1,b, Ling Qi 1,c , Dai Yi-hua 2,d,
Du Cheng-peng 3,e
1) Department of Mechanical Engineering, Hohai University,
Jiangsu Province, Nanjing, 210098, China 2) Yunnan Huaneng Lancangjiang River Hydropower CO.,LTD
Yunnan Province, Kunming, 666100, China
3) Electrical and Electronic Engineering, University of Hongkong,
HK, P.R.China a) [email protected]
Keywords: thermal creep stress, FEM, hydroelectric station, plant, mass concrete,
simulating calculation, anti-cracking
Abstract: This study is mainly in temperature-control and anti-cracking of plant concrete in
hydroelectric station. By means of FEM of three-dimension thermal creep stress and imitating
construction progress, an emulator calculation is performed from construction period to operation
period and distribution regularity of thermal creep stress is brought to light in the theory. The text
described the developing process of concrete’s temperature and thermal stress, and then combined
concrete’s time-varied thermotics and mechanics performance to analyze the possibility of yielding
crack in different period and position.
1 Introduction
1.1 Research background
It is all known that generation of electric is the main purpose of establishing hydroelectric
station. Hydroelectric station’s plant is the essential building in every project whatever the type of
dam is. Due to all kinds of causes, in long-period, peoples don’t afford such enough value to
anti-cracking of plant concrete as to dam. However, because of the complexity of the structure of
plant and limiting in capability and speed of computers and study means, the research of
temperature-control and anti-cracking of plant concrete is almost a blank in all course of concrete
construction.
This study is mainly in temperature-control and anti-cracking of plant concrete in hydroelectric
station. By means of FEM of three-dimension thermal creep stress and imitating construction
progress, an emulator calculation is performed from construction period to operation period and
Key Engineering Materials Vols. 340-341 (2007) pp 1163-1168Online available since 2007/Jun/15 at www.scientific.net© (2007) Trans Tech Publications, Switzerlanddoi:10.4028/www.scientific.net/KEM.340-341.1163
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP,www.ttp.net. (ID: 131.188.31.165, Universitaetsbibliothek Erlangen-Nuernberg, Erlangen, Germany-16/03/14,23:10:46)
distribution regularity of thermal creep stress is brought to light in the theory. In addition, according
the different period and position of thermal creep stress, it forecasts position and time to yield
cracks for offering foundation to adopt necessary measures beforehand in construction.
Fig.1 Diagrammatic Drawing of Finite Element Grids Fig.2 Abaci of Water Temperature of Reservoir
1.2 Introduction of the engineer example and study method
The max height of the RCC gravity dam is 140m. There are 5 electric generating sets in main
power plant and each of those has 350MW equipped capacitor. The concrete of plant use the form
of construction work of dividing dam body into layers and blocks to pour with longitudinal joints
during about the period of 2 years.
Due to the discreteness of the position of elements and nods in subdividing the grid, the author
generator the special preceding processes to imitate the course of plant concrete construction. Major
total of finite elements is 18088 and number of nodes is 85848(refer with: Fig.1). Furthermore,
because half bandwidth is so big that it is necessary to use a very large size of array to memorize
stiffness matrix, this study is processing in mainframe computer by Internet. It takes more 100 CPU
hours to calculate one program from construction period to operation period that is hardly
achievable in usual personal computer.
2 Analysis of water temperature of reservoir[1]
Before calculating thermal stress of plant concrete, it should figure out quasi-stationary
temperature field as initial position of temperature difference calculation. And water temperature of
reservoir of water intake is essential boundary condition. For describing distribution of water
temperature of reservoir as accurately as possible, the author use numeric analysis method to
calculate water temperature of reservoir in operation period. In calculation it considers not only
hydrographical and meteorological of reservoir area, such as atmospheric temperature, cloud cover,
evaporating capacity, wind velocity, solar radiation and water flux, but also operation situation after
498
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10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0 28.0
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC
Temperature(℃)
Elevation (m)
1164 Engineering Plasticity and Its Applications
reservoir constructed, including diversion flux of power station, discharge situation of each
discharge opening and variation of water-lever etc. The result of numeric analysis of water
temperature of reservoir refers with Fig. 2.
3 Analysis of temperature field of plant concrete
3.1 Quasi-stationary temperature field
Quasi-stationary temperature field reflects temperature situation of plant concrete in operation
period. The paper uses three-dimension FEM to study quasi-stationary temperature field of plant
concrete in operation period and offers reliable initial position to calculate temperature difference in
emulator calculation of thermal creep stress. The boundary condition of calculation is atmospheric
temperature of cyclic variation each month in one year and water temperature of upstream reservoir
of corresponding penstock elevation in power station. Considered consistency of emulator
calculation of thermal creep stress, the author adopts the same quantity of elements and nodes of
quasi-stationary temperature field with those of construction emulator calculation.
In this paper it offers representatively typical quasi-stationary temperature field of cross section
on February (refer with: Fig.3, Fig.4). In the figures it is observed that temperature field variation of
concrete in operation period mainly depends up atmospheric temperature of cyclic variation in one
year and water temperature of upstream reservoir. Its depth of influence is about 8m ~10m area in
which temperature-varied-gradient is bigger; the longer the distance to boundary is, the smaller
variation of temperature is. The distribution of quasi-stationary temperature field of plant concrete
in operation period is very complex and closely related to boundary condition of cross section.
Concrete temperature is about 14℃ in the places of volute, pier, elbow-pipe and taper-pipe where
are influenced by water temperature of reservoir on February when it is about 20℃ in mass
concrete. According to the result of calculation, quasi-stationary temperature field on February is
the least so that we use it as initial position of temperature difference calculation.
Z (m) Z (m)
Y (m) X (m)
Fig.3 Quasi-stationary Temperature Field
of X-cross section in the Direction of Dam Axis (℃)
Fig.4 Quasi-stationary Temperature Field
of Y-cross section in the Direction of flow (℃)
Key Engineering Materials Vols. 340-341 1165
3.2 Temperature field of plant concrete in construction period
In construction period concrete temperature is obviously influenced by external atmospheric
temperature. In winter temperature of boundary area where contacts with atmosphere is lower due
to action of atmospheric temperature, however, inner temperature of mass concrete is higher in the
same cross section(refer with: Fig.5). In summer, because of high external temperature, concrete
temperature increases from surface to inner (refer with: Fig.6). As a consequence, it is necessary to
adopt some corresponding proper measures to reduce concrete temperature so as to avoid causing
crack by reason of over temperature difference.
4 Emulator analysis of thermal creep stress field of plant concrete
The paper studies thermal creep stress including 2nd-stage concrete from construction period
to operation period in order to learn thermal stress distribution law of entire plant, especially in the
combining site of volute concrete, old pouring concrete and new pouring concrete. In calculation
aim at different material parameter of 1st-stage and 2nd-stage concrete it uses the cooling-down
method by pouring water and takes into account different cooling water temperature, space
between cooling water pipes, water flow and measures of surface protection. It is observed that
there is an area of large tension stress on the interface between 1st-stage and 2nd-stage concrete in
Fig.7. Because it began to pour 2nd-stage concrete after 1st-stage concrete had poured for a long
time, in this time 1st-stage concrete have reached such high Young’s modulus and strength that it
suffered strong restrain to new pouring 2nd-stage concrete and as a result probably led to generate
crack in the position.
Because thermal creep stress of plant concrete is very complex, peoples don’t fairly
understand distribution situation of stress. Some engineering set enclosed blocks in mass concrete
above plant outlet port in order to release thermal stress suffered by over strong restrain(refer with:
X (m)
Y (m)
X (m)
Y (m)
Fig.5 Temperature Field of Horizon Plane
at 520m Elevation on 30th, January (℃)
Fig.6 Temperature Field of Horizon Plane
at 527m Elevation on 30th, June (℃)
1166 Engineering Plasticity and Its Applications
Fig.8). However, from the result of emulator calculation it is learned that the max stress of
concrete is not yielded in the position of enclosed blocks but in mass concrete above elbow tubes.
It is found that enclosed blocks cannot completely solve the problem that the max stress of plant
concrete is very big and the key point which controls temperature should put in mass concrete
above elbow tubes. Otherwise, in Fig.9 it is observed that tension stress of pier is big because of
external atmospheric temperature and stress concentration which structure shape leads to.
The result of calculation shows that thermal stress of plant concrete is closely related to
structure shape and pouring procedure. Serious stress areas are basically near pier and porthole
located in strongly confined region where is double effected by structure shape and boundary
temperature gradient. In the study it is found that without surface protection calories back-draught
is so serious that the situation of cooling has improved insignificantly in sweltering area. However,
it is a kind of the best controlling temperature measure to adopt cooling-water pipes but due to the
reasons mentioned above the effectiveness of cooling-water pipes is not obvious. In case of setting
surface protection, the effectiveness of pouring cooling-water is better than without it. If diurnal
X
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σ1(第587天)
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-15 -10 -5 0 5 10 15
σ1(第1天)
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-10 -5 0 5 10 15 20 25 30 35 40
σ1(第495天)
-15
-10
-5
0
5
10
15
Fig.7 Stress Field of Y-cross Section in the Direction
of Flow on 587th Day in Construction Period (0.1MPa) Fig.8 Stress Field of X-cross Section in the Direction
of Dam Axis in Operation Period (0.1MPa)
Fig.9 Stress Distribution Chart of Horizon Plane at 506.4m Elevation (0.1MPa)
X Y
Y
Key Engineering Materials Vols. 340-341 1167
amplitude and solar radiation of job location are very big, it should aggravate drying shrinkage of
concrete surface and this time it can take pouring cooling-water with concrete surface protection as
main way of controlling temperature.
5 Summary
Because thermal creep stress is main cause to leading to yield cracks in mass concrete, it can
forecast position and time of generating cracks and take corresponding measures in advance if we
learn distribution regularity of thermal stress in hydroelectric station plant. The main goal of the
study is to point variation regularity of temperature and thermal stress in concrete of hydroelectric
station according to theoretical analysis and adopt measures to controlling temperature with a
definite object and offer exact and practical achievements to engineering.
Reference
[1]. Ding Baoying, Hu Ping, Huang Shuping: The Approximate Analysis for Temperature of
Reservoir water. Journal of Hydroelectric Engineering, Vol.4 (1987)
1168 Engineering Plasticity and Its Applications
Engineering Plasticity and Its Applications 10.4028/www.scientific.net/KEM.340-341 Genetic Analysis of Concrete Crack in Hydroelectric Station's Plant Based on FEM 10.4028/www.scientific.net/KEM.340-341.1163
