Neighborhood, topography, and wind direction effects on wind pressure

distribution on the low-rise building roof

VITOR G. O. CAMILO, MARCO D. DE CAMPOS

Institute of Exact and Earth Sciences

Federal University of Mato Grosso,

Av. Valdon Varjão, 6390, Barra do Garças, 78605-091, Mato Grosso

BRAZIL

Abstract: Low-rise buildings are the majority of the houses that are constructed all over the world.

Experiments of the wind loads acting on these buildings provide vital information to design secure structures

sloped pitched roof structure. The results showed good concordance with the literature. The pressure

coefficients were analyzed, as well, in the flow visualization, highlighting the attachment points and the

recirculation zones.

Key-Words: Wind action, low-rise buildings, neighborhood, wind incidence, topography, pressure coefficients.

Received: November 26, 2021. Revised: October 29, 2022. Accepted: November 25, 2022. Published: December 31, 2022.

1 Introduction

The most common building type used in the

residential, commercial, and industrial sectors is,

arguably, low-rise buildings [1]. Nonetheless, this

construction typically receives low priority and

roof structure provides crucial lateral support to

load-bearing and non-load-bearing walls. Once the

roof structure is partially or fully lost and the roof

diaphragm committed, then with the stand wind

pressure, there is a considerable reduction in the

ability of the walls [2]. Large fluctuating wind loads

originating from turbulent background winds

pronounced flow separation at sharp edges of

buildings (e.g., eaves and building corners), and

intermittent flow separation and reattachment on

structure with double slopes, according to Fouad et

al. [4]. On remaining applications also calculated

the pressure coefficients for two and three buildings

with gabled roofs. The basic parameters considered

in the analysis include neighborhood conditions and

wind direction.

with numerical tests around the contour of buildings

with gable roofs, considering diverse neighborhood

conditions such as the number and geometric

technique validation, according to Fouad et al. [4],

the models were placed inside the domain of 9 H

width, 9H height, and 21H length (Fig. 1f). Here, H

conjunction with the different angles of wind

incidence, was adopted as the control volume,

according to Franke et al. [5]. The boundaries are

5H from the inlet and both sidewalls, 6H from the

for simulations.

Fig. 1 (a-e) Geometry and different angles of

incidence of the wind, and (f), (g) the control

volume.

Table 1. Boundary conditions and nondimensional

parameters.

3 Numerical applications

two directions, and the two inclinations meet at the

ridge. The gable roof is permissible on any

of 6.6 m, a width of 6.6 m, a gable height of 6 m,

and a roof slope equal to 26.6° [4]. The mesh

formed by tetrahedrons resulted in 2331763

elements and 489871 nodes. Here, 1.225 kg/m3 for

air density and a wind speed of 44.76 m/s incidents

at 0° were adopted orthogonally to the side face of

isobaric lines [4] and those generated by Ansys in

this work. The pressure distribution values on the

facades and roof are the same, with a slight change

in distribution. The windward face of the building

presented external pressure coefficients ranging

from 0.20 to 0.98 (Fig. 1a), in line with Fouad et al.

[4], whose values ranged from 0.00 to 1.00 (Fig.

2b). The values range between -0.85 and 0.07 (Fig.

2c) diverge from Fouad et al. [4] on the leeward

Then, to determine significant differences

between the present work results and the literature,

the T-test was used, considering a null hypothesis

that the means are not different. Thus, considering a

one-tailed distribution, p-value=0.43 was obtained

for a critical t=1.81. As 0.43<1.81, it was possible to

conclude that the difference between the mean

values of Cpe is insignificant.

faces had the highest overpressure zones, with the

wind perpendicular to the buildings. The external

pressure coefficients are negative on the faces

between the buildings (Fig. 4f). As a result of wind

funneling between very close edits and accelerating

the airflow, the Venturi effect generated these

suctions. When the wind reaches the first building,

the base and top vortices form on the roof.

Consequently, the flow acceleration originates in an

intense suction region in the inner part of the ridge

corners, mainly in the building where the wind hit

first, showing the maximum coefficient contours of

positive pressure there. In addition, there was the

formation of top vortices with conical shapes, which

The top vortices in the incidence of the wind at the

edge of the eaves caused this suction [8].

Fig. 6. Intense suction region on the corner of the

eaves (detail).

wind speed value grows with height; furthermore,

topographical features such as escarpments in flat

open terrain have a quite strong impact on wind

effect (Fig. 7a). The incidence of wind on a hill or

slope causes the increase of the velocity of flow due

to the Venturi effect. This effect will be maximum

for the wind blowing perpendicular to the ridge line

shows this phenomenon with the streamlines, and it

is possible to observe the gain in wind velocity

along the runoff and the increase in height,

generating intense suctions on the ridges of the roofs

of the buildings arranged on the second slope.

on the right side at ground level received the direct

incidence of the wind (Fig. 7c).

Also, in this case, the Venturi effect generated an

increase in the runoff velocity (Fig. 7d), causing the

highest overpressure regions in the buildings on the

second and third slopes on the left side, with intense

suction on the roof of the building on the summit

(Fig. 7c).

On the right side of the flow, the direct incidence

of the wind on the first building generated intense

other depths in the slopes, the largest zones of

overpressure were found in the lateral faces of the

windward buildings, being the most expressive in

the left edification, and there was a greater region of

turbulence and vortex shedding.

For edits to the right, we have the smaller

overpressure zones resulting from lower incident

wind speed (Fig. 7e-f).

of the buildings at the top of the slope.

runoff velocity.

edges of the slope, and the buildings.

causing intense suctions on the edges of the eaves

and ridges of the roofs and, in a certain way,

increasing the chance of roof collapse and total or

partial destruction of the roofing (Fig. 7g-h).

The distribution of the pressure coefficients

showed that the shielding effect protected the

building on the left side of the slope. On the other

hand, the building to its right presented positive

the roof due to the direct incidence of the wind with

higher velocity (Fig. 7h).

geometric configuration of buildings on the ground,

in conjunction with the different angles of wind

incidence and topography obtained from Ansys

Workbench software.

For validation methodology, a single structure

with double slopes, according to [4], was

considered. In the leeward face, the comparison of

the distribution of isobaric lines showed a

difference.

The values coincided in the windward facade and

the roof. Three orthogonal incidences for low-rise

the two-building model. However, there were the

highest suction zones noticed in these conditions.

This effect is to the leeward vortices in the first

building and the flow interference in the wake.

Now, when the wind is at 45° and the third

building, there was an increase in areas with higher

pressure coefficients compared with the two-

building model. In this case, the most intense

suction zones occurred in the corners of the eaves of

the buildings. Furthermore, with the wind at 90° in

two buildings, the largest overpressure zones were

formed on the windward face of the building when

intense suction.

With the incident wind at 135°, similar to the

wind blowing at 45º, intense overpressure zones

occurred at the corners, mainly in the building

where the wind hit first. In addition, there was the

formation of top vortices with conical shapes. The

third building to leeward received the direct

incidence of the wind, and it was possible to notice

the random development of positive and negative

contours. The other part suffered from the impact of

Finally, to incident wind at 180°, the front facades

of the two buildings on the windward side showed

large overpressure areas. The Venturi effect caused

the flow to gain speed, generating suction on the

internal side faces and originated zones of intense

overpressure in the leeward building, where the

pressure coefficient reached 1.2.

Besides, the topography influenced slopes and

aligned buildings. In this case, the wind blowing