Determining the wind load

With the detailed instructions from OBO, you can easily calculate the wind load and effects on buildings and systems. Try it out now.

We at OBO Bettermann have extensive expertise in the area of wind loads in relation to external lightning protection. Today’s calculation models and air-termination rod systems are the result of numerous studies and years of R&D experience.

The previous German standards in this area – DIN 1055:2005 Part 4: Wind loads and Part 5: Snow and ice loads, and DIN 4131: Steel antenna mounts – dealt with all load assumptions for mounts in Germany.

The Eurocodes (EC) are the result of European standardisation in the construction field. EC 0 to EC 9 cover the documents in the series DIN EN 1990 to 1999. These are supplemented by the various national annexes (NA). The NAs contain provisions that go beyond the Eurocode rules, i.e. the provisions that were previously part of the national standards.

Following the publication of the national annexes to the ECs, the old standards became invalid, following appropriate coexistence phases.

Example of German national standards for the calculation of wind load

Old standard	New standard
DIN 1055:2005-03 Part 4: Wind loads	Eurocode 1: DIN EN 1991-1-4:2010-12: Parts 1–4: General effects; wind loads + DIN EN 1991-1-4/NA: 2010-12
DIN 1055:2005-03 Part 5: Snow and ice loads	DIN EN 1991-1-3: 2010-12 -; Parts 1–3: General effects; snow loads + DIN EN 1991-1-3/NA: 2010-12
DIN V 4131:2008-09 Steel antenna mounts	Eurocode 3: DIN EN 1993-3-1: 2010-12: Parts 3-1: Towers, masts and chimneys – Towers and masts + DIN EN 1993-3-1/NA: 2010-12

1st step 2nd step 3rd step 4nd step

1st step: Determining the wind zone

The second factor that needs to be known when determining the wind load is the wind load zone in which the object is located.
The standards contain no statements regarding the following aspects:

Framework masts and towers with non-parallel main legs,
Stayed masts and chimneys,
Cable-stayed and suspension bridges,
Torsional vibrations.

Zone	Wind speed in m/s	Speed pressure in kN/m²
1	22.5	0.32
2	25.0	0.39
3	27.5	0.47
4	30.0	0.56

2nd step: Determining the terrain category (TC)

Terrain-specific loads and dynamic pressures are an important element in calculating wind loads.

Terrain categories according to DIN EN 1991-1-4

Terrain category (TC)	Definition
Terrain category I	Open sea; lakes with at least 5 km of open water in the wind direction; even, flat land without obstacles
Terrain category II	Terrain with hedges, individual farmsteads, buildings or trees, e.g. agricultural area
Terrain category III	Suburbs, industrial or commercial areas; forests
Terrain category IV	Urban areas in which at least 15% of the area is built up with buildings whose average height is higher than 15 m

3rd step: Determining the maximum gust speed

The tilt and slip resistance of air-termination rods must always be determined on a project-by-project basis. The reference height is the building height and two thirds of the length of the air-termination rod. The maximum gust speed at the project location must be determined.

Gust speed in wind zone I

Reference height in metres	TC I in kph	TC II in kph	TC III in kph	TC IV in kph
0	112	105	100	93
5	122	108	100	93
10	136	124	103	93
16	136	124	111	93
20	139	128	115	98
30	145	134	122	106
40	149	139	128	112
70	157	148	139	126
100	162	155	147	135

Gust speed in wind zone II

Reference height in metres	TC I in kph	TC II in kph	TC III in kph	TC IV in kph
0	124	117	111	104
5	136	120	111	104
10	145	131	114	104
16	152	138	123	104
20	155	142	127	109
30	161	149	136	118
40	165	154	142	125
70	174	165	155	139
100	180	172	163	150

Gust speed in wind zone III

Reference height in metres	TC I in kph	TC II in kph	TC III in kph	TC IV in kph
0	137	129	122	114
5	149	132	122	114
10	159	144	126	114
16	167	152	135	114
20	170	156	140	119
30	177	164	149	129
40	182	170	156	137
70	192	181	170	153
100	198	189	180	165

Gust speed in wind zone IV

Reference height in metres	TC I in kph	TC II in kph	TC III in kph	TC IV in kph
0	149	140	133	124
5	163	144	133	124
10	174	157	137	124
16	182	166	148	125
20	186	170	153	130
30	193	179	163	141
40	198	185	170	150
70	209	198	185	167
100	216	206	196	180

4th step: Determining what concrete blocks are required

Based on the maximum gust speed, the number and size (10 or 16 kg) of concrete blocks required can be determined for the air-termination rod used. The value in the tables must lie above the maximum gust speed for the location.

An example

The maximum gust speed at the location is 142 km/h.

A tapered pipe air-termination rod of type 101 VL2500 and a height of 2.5 m is used.

Because the value in Table 2.15 must be higher than the maximum gust speed at the location (i.e. in this case more than 142 km/h), the next possible value is 164. Three concrete blocks, each of weight 16 kg, must therefore be used.

Number of concrete blocks for tapered pipe air-termination rods

Air-termination rod height in m	1.5	2	2.5	3	3.5	4	Required concrete blocks
Type	101 VL1500	101 VL2000	101 VL2500	101 VL3000	101 VL3500	101 VL4000
Item no.	5401 98 0	5401 98 3	5401 98 6	5401 98 9	5401 99 3	5401 99 5
Wind speed kph	117	-	-	-	-	-	1x 10 kg
Wind speed kph	164	120	95	-	-	-	2x 10 kg
Wind speed kph	165	122	96	-	-	-	1x 16 kg
Wind speed kph	-	170	135	111	95	-	2x 16 kg
Wind speed kph	-	208	164	136	116	102	3x 16 kg

Number of concrete blocks for air-termination rod, one end rounded

Air-termination rod height in m	1	1.5	2	2.5	3	Required concrete blocks
Type	101 ALU-1000	101 ALU-1500	101 ALU-2000	101 ALU-2500	101 ALU-3000
Item no.	5401 77 1	5401 80 1	5401 83 6	5401 85 2	5401 87 9
Wind speed kph	97	-	-	-	-	1x 10 kg
Wind speed kph	196	133	103	-	-	1x 16 kg
Wind speed kph	-	186	143	117	100	2x 16 kg
Wind speed kph	-	-	173	142	121	3x 16 kg

Number of concrete blocks for air-termination rod, one end rounded with connection strap

Air-termination rod height in m	1	1.5	Required concrete blocks
Type	101 A-L 100	101 A-L 150
Item no.	5401 80 8	5401 85 9
Wind speed kph	100	-	1x 10 kg
Wind speed kph	192	129	1x 16 kg
Wind speed kph	-	177	2x 16 kg
Wind speed kph	-	214	3x 16 kg

Number of concrete blocks for insulated VA and Al air-termination rods

Air-termination rod height in m	4	6	4	6	Required concrete blocks
Material	VA	VA	Al	Al
Item no.	5408 94 2	5408 94 6	5408 94 3	5408 94 7
Item no. of appropriate air-termination rod stand	5408 96 8	5408 96 9	5408 96 6	5408 96 7
Wind speed kph	120	94	120	92	3x 16 kg
Wind speed kph	161	122	163	122	6x 16 kg
Wind speed kph	194	145	197	147	9x 16 kg
Wind speed kph	222	165	227	168	12x 16 kg
Wind speed kph	246	182	252	187	15x 16 kg

Number of concrete blocks for insulated air-termination rods with exit

Air-termination rod height in m	4	6	8	10	Required concrete blocks
Item no.	5408 93 8	5408 94 0	5408 88 8	5408 89 0
Item no. of appropriate air-termination rod stand	5408 93 0	5408 93 2	5408 90 2	5408 90 2
Wind speed kph	110	85	93	82	3x 16 kg
Wind speed kph	148	111	116	102	6x 16 kg
Wind speed kph	178	132	134	119	9x 16 kg
Wind speed kph	204	151	151	133	12x 16 kg
Wind speed kph	227	167	166	146	15x 16 kg

Number of concrete blocks for isFang air-termination rod with VA tripod

Air-termination rod height in m	4	4.5	5.0	5.5	6.0	6.5	7.0	7.5	8.0	Required concrete blocks
Item no. of air-termination rod	5402 86 4	5402 86 6	5402 86 8	5402 87 0	5402 87 2	5402 87 4	5402 87 6	5402 87 8	5402 88 0
Item no. of appropriate air-termination rod stand	5408 96 8	5408 96 8	5408 96 8	5408 96 8	5408 96 9	5408 96 9	5408 96 9	5408 96 9	5408 96 9
Wind speed kph	143	124	110	99	104	96	89	83	78	3x 16 kg
Wind speed kph	193	168	148	133	138	127	117	109	102	6x 16 kg
Wind speed kph	232	202	178	159	165	151	139	129	121	9x 16 kg
Wind speed kph	266	231	203	182	188	172	159	147	138	12x 16 kg
Wind speed kph	296	257	226	202	208	191	176	163	152	15x 16 kg

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