فهرست مطالب اکبر رستم پورهفتخوانی

Given the importance of measuring tree volume and the potential for selling standing trees, as well as the time-consuming and costly nature of measuring the actual volume of trees, this study aimed to find an alternative method that is more economical in terms of time and cost for predicting the standing volume of poplars (Populus deltoids) using an artificial neural network (ANN) method for harvesting and sales management. In this study, the diameters and heights of 416 randomly selected trees were measured. The tree diameters ranged from 10 to 15, 15 to 20, 20 to 25, 25 to 30, 30 to 35, 35 to 40, 40 to 45, and 45 to 50 centimeters. Their standing volumes were then predicted using both simple and multiple ANN models. In this study, diameter at breast height and height were considered predictor indices for the input data, while the standing volume of the tree was the output data. The number of input, hidden, and output layers was kept uniform at one layer. The number of hidden layer neurons was determined to be 10 using trial and error. The results showed that the simple ANN model using the diameter index yielded MAPE and R-squared values of 10.22 and 0.9785, respectively, while the model using the height index produced MAPE and R-squared values of 35.43 and 0.8004, respectively. Due to the simple model's ability to predict volume with an error of approximately 10% using the diameter predictor, the simple model with the diameter index was suggested as the best model overall, considering its ease of implementation and superior accuracy.

In this study, bending performance of the WPC profiles of Asre Honar company were measured, then were predited by finite element method (FEM) with ANSYS software to decrease the cost and time of measurement. Therefore, the bending strength of small control specimens with a span length of 180 mm were firstly measured. Accordingly, their bending modulus of elasticity (MOE) and Poisson's ratio of 0.3 were used as input data for prediction. Therefore, four types of hollow and solid WPC profiles with span lengths of 180 and 450 mm were tested under three-point bending loading with a Hounsfield 0308 testing machine with a loading rate of 5 mm/min. Subsequently, their MOR and creep values were measured and compared with those predicted by the FEM. The results of the analysis of variance (ANOVA) Table showed that the main effect of profile types on MOR was statistically significant. Furthermore, the main and the interaction effects of the span lengths and profile types on MOE were statistically significant. The investigation of the main effects revealed that MOR and MOE decreased by 8.8% and increased by 17.7%, respectively by raising the span length from 180 to 450 mm, and also they altered by 33.1% and 24.2% with the change in profile types. In addition, the interaction effects showed that MOR and MOE values changed by 43.9% and 66.6%, respectively with the simultaneous change of the span lengths and profile types. The results indicated that the FEM predicted the MOR values with a mean absolute percentage error (MAPE) of less than 3.03% and their corresponding creep with a MAPE of less than 15.25%. According to the satisfied MAPE of FEM, it could be suggested as an efficient method for predicting the bending properties of these products.

Cabinets doors are usually made of medium-density fiberboard (MDF) as mitered frames connected with wooden dowels, biscuits, spline, or plastic keys with adhesive. Because of its rapidly curing and working, cyanoacrylate adhesive is usually used to connect frame members, but they separate after a while due to its brittle fracture, which is an unusual joining method. Therefore, this study was aimed to investigate the effects of Spline material (plywood, fiberboard, and poplar wood), type of adhesive (polyurethane (PU), and Polyvinyl acetate (PVAc)) with and without a mechanical fastener such as screw on the bending moment capacity of the mitered frame corner joints under diagonal tensile, then compared with frames cut with CNC. Loading was applied with a Hounsfield 0308 testing machine with a loading rate of 5 mm/min. The results showed that the changing of the spline materials, adhesive types, and mechanical fastener resulted in 79.2%, 69.1%, and 131.7% change in the strength of the joints, respectively. The least bending moment was observed in joints made with plywood spline and PU adhesive without any screw; on the contrary, the highest bending moment was related to both joints made with fiberboard and poplar spline with PU adhesive and screws (50.83 and 48.48 N.m, respectively). Late two mentioned joints tolerated higher bending moments than the CNC cut MDF frames (12.4% and 7.6%, respectively). Therefore, all frames are necessary to use spline with PU adhesive as well as screws to make the frame, to reduce the MDF offcuts caused by CNC cutting.

In this study, the strengthening of cross-laminated timber (CLT) with glass fiber reinforced polymer (GFRP) on the lateral resistance (LR) of the single shear lap joints was investigated. Poplar (Populus alba) layers were used to construct the three-layer CLT. In first step, the effect of GFRP strengthening of CLT panel with three layers of FRP fastened with a lag screw, concrete screw, wood screw, and steel nail at an end distance of 1 cm on the lateral load capacity was investigated. In second step, the effect of the number of GFRP layers on the LR of the joint assembled with the lag screw with an end distance of 1 cm was investigated. Finally, the main effects of panel strength directions (major and minor axes), fastener types (lag screw, concrete screw, wood screw, and steel nail), and end distances (1and 2 cm) and their interaction on LR were investigated. The results showed that LR was increased by 22 to 53% with reinforcement, which was more considerable in joints with smaller diameter fasteners. By increasing the number of GFRP layers from one to three layers, LR was increased by 27%. By increasing the end distance, changing the fastener types and panel directions, LR was changed 114.7%, 219.6%, and 7%, respectively. The interaction of variables on LR showed that by simultaneously changing the fastener types × end distance, LR changed about 447%, which implied the importance of choosing the proper fastener with sufficient end distance to construct the joints with a metal connector such as brackets.

The aim of this study was to improve the joints of the mitered furniture frames by using the densified poplar dowels (Populus alba) instead of beech dowels. Therefore, the effects of the dowel number (one and two dowels), dowel diameter (8, 10, and 12mm), and compression ratio (0, 15, and 30%) on bending moment capacity of L-shaped frame corner joints constructed of medium-density fiberboard (MDF) under diagonal tension load were investigated. Then, their performance was compared with those manufactured with beech dowels. Polyvinyl chloride (PVA) was used for gluing the joints. Diagonal loading was performed by Hounsfield (model No. 0380) testing machine with a 5 mm/min loading rate. The results revealed that the bending moment capacity of joints was increased 105.5, 54.3, and 28.75% respectively with the increase of the dowel number, dowel diameter, and compression ratio. The highest bending moment capacity was observed in the joints made out of two 30% compressed dowels with a diameter of 10 mm, and the least of them were seen in joints constructed of one uncompressed dowel with a diameter of 8 mm. the comparison of the joints dowelled by poplar with beech showed that the difference among the bending moment capacity of joints made of poplar dowels with 30% compression ratio and beech dowels was very small (less than one percent), which indicates usability of the densified poplar dowels instead of beech ones.

This study aimed to predict water absorption (WA) and swelling of heat-treated silver fir wood (Abies alba) at 180, 200, and 220 oC by simple regression, multiple linear regression, as well as multiple non-linear regression models. ∆E (total color difference), ∆L (lightness difference), contact angle (CA), and mass loss (ML) were used as predictors. The results showed that WA, volumetric swelling (SV), swelling in longitudinal, radial, and tangential directions (SL, SR, and ST) decreased with the increase of heat-treatment temperature, but the values of ∆E, ∆L, CA, and ML increased. The lowest mean absolute percentage error (MAPE) for the prediction of WA with the simple regression models was related to the Cubic model based on ML equal to 6.22. The lowest MAPE for the prediction of SV, SR, and ST were related to the Cubic model based on ML equal to 3.01, 3.55, and 4.2, respectively. The MAPE values for the prediction of WA, ST, SR, and SV by the multiple linear regression model were 6.11, 3.9, 3.89, and 2.7, respectively. Their corresponding values for the non-linear regression model were 5.76, 3.86, 3.6, and 2.61, respectively. Since MAPE below 10% is satisfactory for predicting, the studied models have predicted WA and their corresponding swelling of heat-treated wood with acceptable accuracy. The best time and cost-efficient regression model is the simple model, and the best predictor in terms of time, cost, and the ability to measure in line is the color index.

Today, several modeling methods have been used to cost-efficiently predict the physical and mechanical properties of wood-based panel products which in turn reduce the cost of quality control of these products. Two common methods include regression and artificial neural network (ANN). In this study, the possibility of predicting the modulus of rupture (MOR) and modulus of elasticity (MOE) of particleboard by simple and multiple linear regression and ANN based on structural parameters including density in three levels (0.65, 0.7, and 0.75 g/cm3), slenderness ratio of particles in three levels (47, 30, and 13) adhesive percent in three level of (8, 9.5, and 11%) were evaluated. experimental and predicted data were compared with different criteria including mean absolute percentage error (MAPE), mean squared error (MSE) and coefficient of determination (R2). The results revealed that although both multiple linear regression models and artificial neural network were able to predict MOR and MOE values with acceptable accuracy, but ANN model predicted them with higher R2 and lower MAPE than multiple linear regression model. The value of MAPE and R2, for prediction of MOR and MOE by ANN model were 7.72% and 0.77, and 7% and 0.86, respectively. the corresponding value for multiple regression model were 8.3% and 0.738, and 9.06% and 0.783, respectively. These levels of error are industrially and practically satisfactory for the prediction of properties in particleboard.

In this study, flexural reinforcement of 3-layer screwed CLT made of poplar (Populous alba) and polyurethane glue was investigated. Static bending test was performed by Instron according to ASTM D4761. The variables of this study were types of reinforcing (aluminum sheet and glass fiber reinforcement polymer (GFRP) wrap) and arrangements of reinforcers (no.1: bonded on the bottom (tension) side; no.2: bonded on the bottom and top (tension and compression side); no.3: bonded on the bottom, top and between two bottom layers; no.4: bonded on the bottom, top and among layers). The results showed that the higher MOR and MOE were related to major direction of CLT reinforced with aluminum with configuration of no.1. The lower MOR and MOE were observed in minor direction of CLT reinforced with GFRP with configuration of no.1. The increasing percentage of the MOR and MOE in minor direction of CLT reinforced with aluminum were 195.1 and 344.6% and in major direction of them were 89.3 and 50.8%, respectively in comparison with control specimens. When CLT panel were reinforced with GFRP, the increasing percentage of MOR and MOE in the minor direction of CLT were 42.8 and 21.3% and in major direction of CLT were, respectively 46.1 and 12.7% in comparison with control specimens. The results showed that MOR and MOE of CLT reinforced with aluminum sheet were higher than those reinforced with GFRP wraps. Failure modes of CLT were changed by reinforcing from brittle to ductile and consequently increased their flexural strength.

In this study, the utilization of fibers recycled from MDF wastes and waste papers for manufacturing fiberboards was investigated. The proportion of waste paper to recycled fibers from MDF wastes was 70/30 and 50/50. Also the effect of utilization of poly vinyl acetate adhesive on properties of boards was investigated. Boards were manufactured at density of 0.3 g/cm3 and dimension of 30×30×1.2cm. Practical properties of boards including thickness swelling, bending strength, modulus of elasticity and internal bonding were measured. The results showed that the utilization of adhesive can improve all of board properties. Change in proportion of recycled fibers to waste paper had different influences on various properties of manufactured fiberboards. The proportion of 70/30 of waste paper to recycled fibers from MDF wastes led to improving bending strength and modulus of elasticity of fiberboards, while the manufactured boards from proportion of 50/50 had better results about thickness swelling and internal bonding. Overall, it can be concluded that recycled fibers from MDF wastes mixed with waste paper can successfully utilize in producing fiberboards.

In this study, flexural performance of cross-laminated timber (CLT) made out of poplar wood (Populus alba), Polyurethane adhesive and different mechanical connectors were investigated. Amount of adhesive was 300 g/m2. For manufacturing CLT panels, wood planks were air-dried, then four face-bonding surfaces of planks were planed (S4S). Thickness and width of planks were 19 and 100 mm, respectively. The thickness, width and span to depth ratio of Three-layered CLT specimens for bending test were 57, 80 mm and 12, respectively. Bending test was conducted by Instron 4486. The variables of this study were including different connectors (galvanized steel nail, strip brad nails (ST Nails) and coarse thread drywall screw), connector number (2 and 4), adhesive (with and without adhesive) and panel direction (major and minor direction). The results showed that the higher modulus of rupture (MOR) and modulus of elasticity (MOE) were related to major direction of CLT panels connected by 4 screws and adhesive as well the lower of them were related to minor direction of CLT panels connected by 2 ST nails and adhesive. The results also showed that MOR and MOE of CLT panels were changed about 71 and 16, 16 and 400, 1 and 10%, respectively with the change of shear connector, adhesive and number of connector. MOR and MOE in major direction of CLT panels were about 3 and 4 times higher than those in minor direction. The results revealed that MOR of CLT panels meet the specified requirements of ISO 16696-1 standard, however, MOE of them were not comparable with standard value. Hence, it was recommended to perform some comprehensive studies for reinforcing CLT panels made of poplar for increasing their MOE.

The aim of this study was to investigate flexural strengthening of screwed Glulam made with poplar (Populus alba). Polyurethane adhesive and screw were used for joining layers and applying pressure for manufacturing of three-layer glulam. The variables of this study were types of reinforcing (galvanized steel, aluminum sheet and glass fiber reinforcement polymer) and arrangements of reinforcing: No. 1 (bonded on the bottom (tension) side); No. 2 (bonded on the bottom and top (Tension and compression) side); No. 3 (bonded on the bottom, top and between two bottom layers); No. 4 (bonded on the bottom, top and among layers). Bending test was conducted by Instron according to ASTM D7341. The highest MOR (82.96 MPa) and MOE (1066.33 MPa) were both observed in Glulams reinforced by galvanized steel sheet with arrangement of No. 2 and the lowest MOR (57.82 MPa) and MOE (4397.33 MPa) were both related to Glulams reinforced by GFRP wrapped with arrangement of No. 1. MOR and MOE of control Glulams were 48.1 and 4330 MPa. The increasing percentage of MOR due to reinforcing by galvanized steel, aluminum sheet and GFRP Wrapped were 72.5, 57.8 and 42.6, respectively. The increasing percentages for MOE were 134.2, 57.6 and 28.4, respectively. Failure modes of Glulams changed from brittle to ductile by reinforcing resulted in improving of flexural behavior. The independent effect of types and arrangements of reinforcing on MOR and MOE and also the interaction of types and arrangements of reinforcing on MOE were statistically significant.

In this study, modulus of rupture (MOR) and modulus of elasticity (MOE) of glued-laminated timber (Glulam) made out of poplar (Populus alba) with galvanized steel nail, brad strip nail, coarse thread drywall screw for applying pressure were investigated and compared with those constructed with cold press. Amount of polyurethane adhesive was 300 g/m2. Thickness, width and span of 3-ply glulam specimens were 57, 80 and 640 mm, respectively. Static bending test was performed according to ASTM D 7341 by Instron testing machine. The results showed that the higher MOR and MOE were related to Glulam connected by 4 screws on 8×8 cm2 with adhesive (69.3 MPa), and those connected by 2 galvanized steel nail with adhesive (6737.7 MPa), respectively. The results also revealed that the lower MOR and MOE were both observed in Glulam connected by 2 brad strip nail without any adhesive (23.9 and 1252.7 MPa, respectively). The results showed that MOR and MOE of glulam were changed with the independent variation of number of fastener 3.7 and ˂1%, respectively. The higher variation was related to independent effect of adhesive (130 and 317.8% for MOR and MOE, respectively). Analysis of variance indicated that only the independent effect of adhesive application was only statistically significant at 95% confidence level. The comparison of MOR and MOE of Glulam made with two fasteners with those constructed by cold press showed that there was not significant difference between them. So, the use of galvanized steel nail, brad strip nail, coarse thread drywall screw for applying pressure to manufacture Glulam instead of cold press is possible and the best item was brad strip nail due to easy application and installation by pneumatic nailer and low cost.

Bending strength is a critical property of cross laminated timber (CLT) in structural applications, especially in floor of multi-story buildings. Therefore, this study was targeted to evaluate bending strength of CLT made out of poplar (populous alba). Polyurethane adhesive was used for constructing of CLT (300 g/m2). The thickness of planks was used in this study was 16 mm. The results have indicated that modulus of rupture (MOR) and modulus of elasticity (MOE) of CLT with 45o alternating transverse layer were increased 14 and 15%, respectively in comparison with 90o layers. Also, modulus of rupture (MOR) and modulus of elasticity (MOE) of CLT consist of layers with 4cm in width were increased 14 and 5%, respectively in comparison with layers 9cm in width. The results concluded that by layers with lower width, and also 45o alternating layer configuration could be constructed CLT from fast growing trees such as poplar with a considerable bending strength.

The goal of this study was to determine stress carrying capacity of doweled corner joints in framed furniture structures. Joint members were out of European silver Fir (Abies alba) and dowels were made from Beech and Hornbeam woods as variables in this study. Diameter of dowel had three levels in size، namely 6، 8 and 10 mm. Mitered and Butted experimental joints were tested under diagonal tension and compression loads. Results have shown that stress carrying capacity of tested joints under compressive load is more than that of tension one. Also، stress carrying capacity of mitered joints، under both loading type، was more than that of butted joints. Maximum stress capacity under tension load was observed in mitered joints with dowels of hornbeam which were 8 mm in diameter. Under compressive loads، maximum stress capacity was determined in mitered joints fabricated with dowels out of beech which were 8 mm in diameter. With tension loading، changing diameter of dowels from 6 to 8 mm، stress capacity of joint did increase drastically but from 8 to 10 mm، had no significant effects on joints’ capacity. Under compressive load، changing diameter of dowels from 6 to 10 mm had significant effect on capacity of joints. Species of dowel’s wood was not effective in tension، but in compression dowels of beech wood had pronounced improvement on joints’ capacity.

This study was conducted to evaluate stress carrying capacity of miter corner joints fabricated with dovetail fitting in frames made with particleboard and medium density fiber board (MDF) under diagonal tension loading. In this study، tests were carried out to determine the effects of dovetail fitting height (9 and 14 mm)، and adhesive types (polyvinyl acetate (PVAs)، cyanoacrylate (CA) on stress carrying capacity of dovetail joints under diagonal tension loading، and the joints without adhesive were compared. The results indicate that stress carrying capacity has increased، with the increase of high dovetail. The stress carrying capacity of joints constructed with CA adhesive was higher than that of those constructed with PVAs and without adhesive. Furthermore، the stress carrying capacity joints constructed with MDF was higher than that of those of particleboard. The lowest ultimate stress carrying capacities (2. 61Mpa) were obtained at 9 mm high dovetail of dovetail joints made of particleboard and without adhesive. Highest bending moment resistance (8. 61Mpa) was observed at 14 mm high dovetail with CA adhesive in medium density fiberboard.

The purpose of this study was to investigate the effects of the screw diameter and pilot holes diameter as well as end distance, thickness of side and main members and screw type on the lateral load of joints made from various screws on commercial wood-plastic composites. Three types of screws, including sheet metal screws with gauges 8, 10, 14 (4, 5, 6 mm, nominally), wood screws with gauge 8 (4mm, nominally), and drywall screws with gauge 8 (4mm, nominally) were used. The results showed that lateral load of joints do not increase continuously with increase of screws diameter and this must be attributed to decrease of net section of joint members. However, with a given diameter of screw, lateral load of joint increased with the increase of end distance, thickness of joint members. Also, results showed that, with the increase of predrilled holes diameter up to root-diameter of screw, lateral load of joint decreased drastically. Concerning screw type effect, the lateral load of joint made using wood screw was higher than joints made with sheet metal and drywall screws.

Withdrawals resistances of screws driven into commercial wood plastic composite (WPC) panels in both face and edge directions have been measured and the results have been compared with those of conventional medium density fiberboard (MDF) and particleboard. Three types of screws namely; sheet metal screw (gauge # 4، 8، 10، 14)، wood screw (gauge #8) and drywall screw (gauge #8) were used. The results have indicated that withdrawal resistances of screws in WPC panels in both directions increase as screw diameter. Similar increases were observed when pilot holes diameter were increased close to the root diameter of the screws. Beyond this limit، increasing the pilot hole diameter up to the nominal diameter of the screws، significantly reduced withdrawal resistance. No significant differences were observed between different types of screw. Face and edge withdrawal resistances of screws in WPC panels were higher as compared with those of MDF and particleboard panels.

Particle size, board density and adhesive content are the most important factors, influencing on physical and mechanical properties of particleboard. In this study the effects of density, adhesive content and particle size on withdrawal strength of particleboard made from Populus (Populus alba) particles have been studied. Three levels of density including 0.65, 0.7, and 0.75 g/cm3, three levels of adhesive content including 8, 9.5, and 11% and four levels of particles size including +5, -5 +8, -8 +12, and -12 mesh were used Moisture content of cake, press time, press temperature, press pressure were 12%, 5 min, 180 oC, and 35 kg/cm2 respectively. The results showed that particle size increased screw withdrawal resistance more than board density and adhesive percent, so there was a possibility to increase screw withdrawal resistance without increasing board density and adhesive percent. The highest withdrawal strength was obtained in particle board with density 0.75 g/cm3, adhesive content 11% and particle size +5 mesh.