STRESS, DISPLACEMENT JOINTS OF GMELINA ARBOREA AND TECTONA GRANDIS WOOD WITH METAL PLATES, SCREWS AND NAILS FOR USE IN TIMBER TRUSS CONNECTIONS

In countries like Costa Rica, there is an interest in developing wooden trusses in a versatile and light way. However, there is a key aspect in the behavior of truss connections in this product. Therefore, the present study determines the structural behavior of the truss connections and the displacement, the resistance, the stiffness values and the failure mode of truss connections made with Gmelina arborea and Tectona grandis timber for angles of 0° and 90°; and three types of truss connectors (metal plates, screws and nails), subject to tension and compression loads. The results showed that metal plates show the highest load values with respect to the nails and screws in both species. Likewise, in the design and critical displacement stress, metal plates surpass the nails and screws in both species; and in the two angles. From these stress values, we proposed a model for the prediction of the stiffness for the truss connections of the intermediate angles (30°, 45° and 60°) and the test showed that the prediction was low, the bias was 3%.

Keywords:
structures; Fastener; Stiffness; Tropical wood; Tropical species

Authorship

Monzerrath Rivera-Tenorio

Instituto Tecnologico de Costa Rica, Costa RicaInstituto Tecnologico de Costa RicaCosta RicaCosta Rica Instituto Tecnologico de Costa Rica, Costa Rica

http://orcid.org/0000-0001-8079-5269

Roger Moya ⁺ + rmoya@itcr.ac.cr

Instituto Tecnologico de Costa Rica, Costa RicaInstituto Tecnologico de Costa RicaCosta RicaCosta Rica Instituto Tecnologico de Costa Rica, Costa Rica

+ rmoya@itcr.ac.cr

SCIMAGO INSTITUTIONS RANKINGS

Instituto Tecnologico de Costa Rica, Costa RicaInstituto Tecnologico de Costa RicaCosta RicaCosta Rica Instituto Tecnologico de Costa Rica, Costa Rica

Figures | Tables | Formulas

Figures (7)
Tables (5)
Formulas (15)

Angle	Gmelina arborea			Tectona grandis
Angle	Moisture content (%)	Density (kg.m^-3)	Moisture content (%)	Density (kg.m^-3)
0°	11.68A	413.62A	10.57A	527.10A
0°	(20.06)	(34.85)	(19.64)	(13.68)
90°	11.30A	444.26A	10.29A	541.20A
90°	(27.90)	(17.87)	(18.14)	(8.28)

Angle	Test	Fastener	Gmelina arborea		Tectona grandis
Angle	Test	Fastener	Design stress (MPa)	Critical displacement stress (MPa)	Design stress (MPa)	Critical displacement stress (MPa)
0°	Compression	Metal plates	10.33A	18.90A	5.07A	22.28A
		Metal plates	Screws	(44.15)	(73.03)	(36.74)
		Screws	5.79B	4.12B	2.86A	3.90B
		Screws	(13.34)	(23.17)	(22.91)	(28.48)
		Nails	4.29C	4.77B	2.76A	15.02C
		Nails	(18.48)	(17.09)	(32.30)	(30.00)
	Tension	Metal plates	15.41A	7.47A	7.05A	4,82A
		Metal plates	(78.11)	(35.43)	(48.02)	(84.73)
		Screws	9.62B	4.15B	3.89B	3.26A
		Screws	(10.27)	(24.69)	(77.03)	(183.27)
		Nails	8.12B	3.39B	3.27B	2.06A
		Nails	(21.55)	(13.95)	(56.51)	(179.04)
90°	Compression	Metal plates	4.22A	12.06A	15.12A	15.21A
		Metal plates	(24.63)	(21.30)	(26.20)	(32.39)
		Screws	2.08B	1.70B	9.73B	12.80A
		Screws	(23.89)	(11.20)	(26.69)	(29.91)
		Nails	2.39B	1.80B	11.45AB	22.34A
		Nails	(32.41)	(25.01)	(102.08)	(95.54)
	Tension	Metal plates	18.68A	3.52A	8.34A	5.50A
		Metal plates	(37.03)	(101.15)	(17.26)	(50.90)
		Screws	6.40B	3.13A	3.99B	1.97B
		Screws	(14.13)	(12.11)	(74.60)	(93.09)
		Nails	8.40C	3.74A	4,17B	2.99AB
		Nails	(25.11)	(27.59)	(54.62)	(95.70)

Species	Test	Metal Plates				Screws				Nails
Species	Test	n	R	Angle	K	n	R	Angle	K	n	R	Angle	K
Gmelina arborea	Compression	1.5	0.9998	30°	13.90	1.75	0.9994	30°	2.75	1.75	0.9997	30°	3.05
				45°	12.38			45°	2.21			45°	2.40
				60°	11.69			60°	1.89			60°	2.02
	Tension	1.5	0.9992	30°	4.80	1.5	0.9998	30°	3.26	1.0	0.9987	30°	2.57
				45°	4.02			45°	3.00			45°	2.51
				60°	3.62			60°	2.92			60°	2.64
Tectona grandis	Compression	1.5	0.9998	30°	16.82	1.75	0.9996	30°	4.49	1.5	0.9998	30°	14.39
				45°	15.19			45°	5.48			45°	15.10
				60°	14.51			60°	7.30			60°	16.77
	Tension	1.5	0.9997	30°	4.32	1.5	0.9998	30°	2.34	1.5	0.9998	30°	1.96
				45°	4.32			45°	2.06			45°	2.05
				60°	4.54			60°	1.93			60°	2.27

Test	Fastener	Angle	Gmelina arborea			Tectona grandis
Test	Fastener	Angle	1.0	1.5	2.0	1.0	1.5	2.0
Compression	Metal Plates	0°	-	-	-	-	-	-
		30°	11.46	13.90	16.55	13.93	16.82	19.95
		45°	10.41	12.38	14.72	12.78	15.19	18.07
		60°	10.18	11.69	13.26	12.59	14.51	16.51
		90°	-	-	-	-	-	-
	Screws	0°	-	-	-	-	-	-
		30°	1.98	2.48	3.04	3.83	4.27	4.72
		45°	1.70	2.02	2.41	4.23	5.03	5.98
		60°	1.59	1.79	1.99	5.10	6.51	8.15
		90°	-	-	-	-	-	-
	Nails	0°	-	-	-	-	-	-
		30°	2.18	2.74	3.38	12.49	14.39	16.36
		45°	1.85	2.20	2.61	12.70	15.10	17.96
		60°	1.71	1.92	2.13	13.88	16.77	19.91
		90°	-	-	-	-	-	-
Tension	Metal Plates	0°	-	-	-	-	-	-
		30°	3.88	4.80	5.83	3.69	4.32	4.97
		45°	3.38	4.02	4.79	3.63	4.32	5.13
		60°	3.20	3.62	4.06	3.82	4.54	5.31
		90°	-	-	-	-	-	-
	Screws	0°	-	-	-	-	-	-
		30°	2.81	3.26	3.84	1.92	2.34	2.80
		45°	2.52	3.00	3.57	1.73	2.06	2.45
		60°	2.52	2.92	3.33	1.69	1.93	2.19
		90°	-	-	-	-	-	-
	Nails	0°	-	-	-	-	-	-
		30°	2.57	1.78	1.78	1.70	1.96	2.23
		45°	2.51	2.99	3.56	1.72	2.05	2.44
		60°	2.64	3.13	3.65	1.88	2.27	2.69
		90°	-	-	-	-	-	-

Species	Fastener	Test	Model for prediction of stiffness for truss truss connection
Gmelina arborea	Metal Plates	Compression	$K_{θ} = 0.0015 * θ^{2} - 0.2115 * θ + 18.892$
	Metal Plates	Tension	$K_{θ} = 0.0007 * θ^{2} - 0.1082 θ * + 7.4506$
	Screws	Compression	$K_{θ} = 0.0003 * θ^{2} - 0.0573 θ * + 4.1297$
	Screws	Tension	$K_{θ} = 0.0003 * θ^{2} - 0.0393 θ * + 4.1503$
	Nails	Compression	$K_{θ} = 0.0004 * θ^{2} - 0.0715 θ * + 4.7768$
	Nails	Tension	$K_{θ} = 0.0005 * θ^{2} - 0.0437 θ * + 3.3960$
Tectona grandis	Metal Plates	Compression	$K_{θ} = 0.0017 * θ^{2} - 0.2335 θ * + 22.266$
	Metal Plates	Tension	$K_{θ} = 0.0004 * θ^{2} - 0.0292 θ * + 4.8207$
	Screws	Compression	$K_{θ} = 0.0014 * θ^{2} - 0.0263 θ * + 3.9277$
	Screws	Tension	$K_{θ} = 0.0003 * θ^{2} - 0.0382 θ * + 3.2478$
	Nails	Compression	$K_{θ} = 0.0170 * θ^{2} - 0.0754 θ * + 15.032$
	Nails	Tension	$K_{θ} = 0.0002 * θ^{2} - 0.0104 θ * + 2.0614$