We studied moist deciduous forests of Chhattisgarh, India(1) to assess the effect of four levels of historic wildland fire frequency(high, medium, low, and no-fire) on regeneration of seedlings in fire affected areas ...We studied moist deciduous forests of Chhattisgarh, India(1) to assess the effect of four levels of historic wildland fire frequency(high, medium, low, and no-fire) on regeneration of seedlings in fire affected areas during pre and post-fire seasons,(2) to evaluate vegetation structure and diversity by layer in the four fire frequency zones,(3) to evaluate the impact of fire frequency on the structure of economically important tree species of the region, and(4) to quantify fuel loads by fire frequency level. We classified fire-affected areas into high, medium, low, and no-fire frequency classes based on government records. Tree species were unevenly distributed across fire frequency categories. Shrub density was maximum in zones of high fire frequency and minimum in lowfrequency and no-fire zones. Lower tree density after fires indicated that regeneration of seedlings was reduced by fire. The population structure in the high-frequency zone was comprised of seedlings of size class(A) and saplings of size class(B), represented by Diospyros melanoxylon, Dalbergia sissoo, Shorea robusta and Tectona grandis. Younger and older trees were more abundant for Tectona grandis and Dalbargia sissoo after fire, whereas intermediate-aged trees were more abundant prefire, indicating that the latter age-class was thinned by the catastrophic effect of fire. The major contributing components of fuel load included duff litter and small woody branches and twigs on the forest floor. Total fuel load on the forest floor ranged from 2.2 to 3.38 Mg/ha. The netchange in fuel load was positive in high- and medium-frequency fire zones and negative under low- and no-fire zones. Repeated fires, however, slowly reduced stand stability. An ecological approach is needed for fire management to restore the no-fire spatial and temporal structure of moist deciduous forests, their species composition and fuel loads. The management approach should incorporate participatory forest management. Use of controlled fire, fire lines and mapping of fire prone areas are fundamental principles of fire hazard reduction in these areas.展开更多
The effects of fire exposure,reinforcement ratio and the presence of axial load under fire on the seismic behavior of reinforced concrete(RC) shear walls were investigated.Five RC shear walls were tested under low cyc...The effects of fire exposure,reinforcement ratio and the presence of axial load under fire on the seismic behavior of reinforced concrete(RC) shear walls were investigated.Five RC shear walls were tested under low cyclic loading.Prior to the cyclic test,three specimens were exposed to fire and two of them were also subjected to a constant axial load.Test results indicate that the ultimate load of the specimen with lower reinforcement ratio is reduced by 15.8%after exposure to elevated temperatures.While the reductions in the energy dissipation and initial stiffness are 59.2%and 51.8%,respectively,which are much higher than those in the ultimate load.However,this deterioration can be slowed down by properly increasing reinforcement due to the strength and stiffness recovery of steel bars after cooling.In addition,the combined action of elevated temperatures and axial load results in more energy dissipation than the action of fire exposure alone.展开更多
Finite element method is employed to calculate the temperature fields for two kinds of steel concrete composite slabs: composite slab with profiled steel sheeting and LJMB composite slab. The calculated results are in...Finite element method is employed to calculate the temperature fields for two kinds of steel concrete composite slabs: composite slab with profiled steel sheeting and LJMB composite slab. The calculated results are in good agreement with those of tests. Fire resistance of the two kinds of composite slabs is calculated by using a numeric method. The results show that: due to heat absorbing of concrete, the performance of composite slabs under fire is better than that of unprotected steel structure, and fire resistance of composite slabs mentioned in this paper is at least 30 min subjected to standard fire. Parameters related to the fire resistance are discussed. It was found that with increasing of concrete strength and thickness of slab, fire resistance increases, and with increasing of steel strength and steel ratio, fire resistance decreases. Also thickness of fire proof is calculated by a numeric method. The results obtained in this paper may be referenced for practical engineering.展开更多
A part load operation by turning the burner on and off intermittently is effective for a small scale direct fired absorption chiller. The dynamic performance of the system has been investigated. The relationship betwe...A part load operation by turning the burner on and off intermittently is effective for a small scale direct fired absorption chiller. The dynamic performance of the system has been investigated. The relationship between pressure, temperature and concentration of the lithium bromide solution have been analyzed. The result obtained indicates that the pressure of the high pressure generator and the temperature of the exhausted smoke are the most sensitive parameters. It is also found that the transition time from a full load to a part load condition is quite long, and part load relative cooling capacity is almost near the intermittent running time ratio and oil consumption ratio.展开更多
基金financed by NRSA,Hyderabad,Forest Department of Chhattisgarh,India
文摘We studied moist deciduous forests of Chhattisgarh, India(1) to assess the effect of four levels of historic wildland fire frequency(high, medium, low, and no-fire) on regeneration of seedlings in fire affected areas during pre and post-fire seasons,(2) to evaluate vegetation structure and diversity by layer in the four fire frequency zones,(3) to evaluate the impact of fire frequency on the structure of economically important tree species of the region, and(4) to quantify fuel loads by fire frequency level. We classified fire-affected areas into high, medium, low, and no-fire frequency classes based on government records. Tree species were unevenly distributed across fire frequency categories. Shrub density was maximum in zones of high fire frequency and minimum in lowfrequency and no-fire zones. Lower tree density after fires indicated that regeneration of seedlings was reduced by fire. The population structure in the high-frequency zone was comprised of seedlings of size class(A) and saplings of size class(B), represented by Diospyros melanoxylon, Dalbergia sissoo, Shorea robusta and Tectona grandis. Younger and older trees were more abundant for Tectona grandis and Dalbargia sissoo after fire, whereas intermediate-aged trees were more abundant prefire, indicating that the latter age-class was thinned by the catastrophic effect of fire. The major contributing components of fuel load included duff litter and small woody branches and twigs on the forest floor. Total fuel load on the forest floor ranged from 2.2 to 3.38 Mg/ha. The netchange in fuel load was positive in high- and medium-frequency fire zones and negative under low- and no-fire zones. Repeated fires, however, slowly reduced stand stability. An ecological approach is needed for fire management to restore the no-fire spatial and temporal structure of moist deciduous forests, their species composition and fuel loads. The management approach should incorporate participatory forest management. Use of controlled fire, fire lines and mapping of fire prone areas are fundamental principles of fire hazard reduction in these areas.
基金Project(200801410005) supported by Doctoral Foundation of Ministry of Education of China
文摘The effects of fire exposure,reinforcement ratio and the presence of axial load under fire on the seismic behavior of reinforced concrete(RC) shear walls were investigated.Five RC shear walls were tested under low cyclic loading.Prior to the cyclic test,three specimens were exposed to fire and two of them were also subjected to a constant axial load.Test results indicate that the ultimate load of the specimen with lower reinforcement ratio is reduced by 15.8%after exposure to elevated temperatures.While the reductions in the energy dissipation and initial stiffness are 59.2%and 51.8%,respectively,which are much higher than those in the ultimate load.However,this deterioration can be slowed down by properly increasing reinforcement due to the strength and stiffness recovery of steel bars after cooling.In addition,the combined action of elevated temperatures and axial load results in more energy dissipation than the action of fire exposure alone.
文摘Finite element method is employed to calculate the temperature fields for two kinds of steel concrete composite slabs: composite slab with profiled steel sheeting and LJMB composite slab. The calculated results are in good agreement with those of tests. Fire resistance of the two kinds of composite slabs is calculated by using a numeric method. The results show that: due to heat absorbing of concrete, the performance of composite slabs under fire is better than that of unprotected steel structure, and fire resistance of composite slabs mentioned in this paper is at least 30 min subjected to standard fire. Parameters related to the fire resistance are discussed. It was found that with increasing of concrete strength and thickness of slab, fire resistance increases, and with increasing of steel strength and steel ratio, fire resistance decreases. Also thickness of fire proof is calculated by a numeric method. The results obtained in this paper may be referenced for practical engineering.
文摘A part load operation by turning the burner on and off intermittently is effective for a small scale direct fired absorption chiller. The dynamic performance of the system has been investigated. The relationship between pressure, temperature and concentration of the lithium bromide solution have been analyzed. The result obtained indicates that the pressure of the high pressure generator and the temperature of the exhausted smoke are the most sensitive parameters. It is also found that the transition time from a full load to a part load condition is quite long, and part load relative cooling capacity is almost near the intermittent running time ratio and oil consumption ratio.
