Dear Mr. Nicolini: Qualitative Pedestrian Level Wind Assessment Montreal Road, Ottawa GWE File No.: DTPLW

Transcription

1 August 17, 2015 Anthony Nicolini Ontario Inc. (Darwin Group) 183 Michael Cowpland Drive Ottawa, Ontario K2M 0M3 Dear Mr. Nicolini: Re: Qualitative Pedestrian Level Wind Assessment Montreal Road, Ottawa GWE File No.: DTPLW 1. INTRODUCTION Gradient Wind Engineering Inc. (GWE) was retained by Ontario Inc. (Darwin Group) to undertake a qualitative pedestrian level wind assessment in support of site plan control and design development for a proposed office building located at Montreal Road in Ottawa, Ontario. Our work is based on architectural drawings provided by Chmiel Architects in August of 2015, consideration of existing and approved future surrounding buildings, and statistical knowledge of the Ottawa wind climate, as well as experience with similar projects in Ottawa. In the early stages of design development, a qualitative pedestrian wind assessment is useful to identify any significant massing features or design elements which may adversely impact pedestrian activities within the study area, and to provide initial mitigation strategies, if required. 127 Walgreen Road, Ottawa, Ontario K0A 1L0 T (613)

2 2. TERMS OF REFERENCE The focus of this qualitative wind analysis is the proposed mixed-use office-retail development located at Montreal Road in Ottawa, Ontario. The study site is situated on the north side of Montreal Road, mid-block between Lang s Road and Codd s Road, east of Ottawa proper, and approximately two (2) kilometers (km) south of the Ottawa River and Rockcliffe Airport. Upon completion, the planned mixed-use development will feature a nine-storey building rising to a maximum height of metres above grade to the top of the mechanical penthouse. The building s rectangular floor plate is maintained on all elevations with its long axis parallel to Montreal Road. The ground floor will contain retail spaces along the south side of the building, while dedicated access to the office lobby is provided on the west side of the building. Levels two through nine are solely served by office spaces. Additionally, a parking structure extends from the north elevation of the building, rising two (2) levels above grade. Of particular importance for pedestrian comfort, the ninth level contains terraces at each of its four (4) corners. Regarding wind exposures, the near-field surroundings of the development (defined as an area falling within a 200 metre (m) radius from the subject site) are characterized by a mix of mostly low and medium height buildings for all wind directions. The far-field surroundings (defined as the area beyond the near field and within a 2 km radius), are characterized by the open exposure of the sparse land and the Ottawa River for northwest clockwise through north-northeast wind directions, while the remaining compass azimuth is defined by a suburban exposure resulting from low-rise dwellings and medium-rise office and commercial developments. A hybrid ground floor / roof terrace plan, inclusive of the letter tags identifying wind sensitive pedestrian locations considered in this assessment, is illustrated in Figure Montreal Road, Ottawa: Qualitative Pedestrian Level Wind Assessment 2

3 3. METHODOLOGY The main aspects of a qualitative pedestrian level wind assessment include: (i) consideration of the statistical properties of the local wind climate; (ii) knowledge of wind flow behaviour in typical urban, suburban, and open environments; and (iii) an understanding of how common wind conditions relate to typical pedestrian activity types Ottawa Wind Climate The statistical model of the Ottawa wind climate, which indicates the directional character of local winds on a seasonal basis, is illustrated on the following page. The plots illustrate seasonal distribution of measured wind speeds and directions in kilometres per hour. Probabilities of occurrence of different wind speeds are represented as stacked polar bars in sixteen azimuth divisions. The radial direction represents the percentage of time for various wind speed ranges per wind direction during a 40-year measurement period. The preferred wind speeds and directions can be identified by the longer length of the bars. For Ottawa, the most common winds concerning pedestrian comfort occur from the south clockwise to the north, as well as those from the east. The directional preference and relative magnitude of the wind speed varies somewhat from season to season, with the summer months displaying the calmest winds relative to the remaining seasonal periods Montreal Road, Ottawa: Qualitative Pedestrian Level Wind Assessment 3

4 SEASONAL DISTRIBUTION OF WINDS FOR VARIOUS PROBABILITIES OTTAWA MACDONALD-CARTIER INTERNATIONAL AIRPORT Notes: 1. Radial distances indicate percentage of time of wind events. 2. Wind speeds represent mean hourly wind speeds measured at 10 metres above the ground Montreal Road, Ottawa: Qualitative Pedestrian Level Wind Assessment 4

5 3.2. Massing vs. Climate Geometric Effects The physical features of a development site that are most influential to the local wind conditions include the massing and relative spacing of surrounding buildings, the geometry and orientation of the study building, and the alignment of the study building with respect to statistically prominent wind directions. Wind flow characteristics which combine to determine how conditions will develop include phenomena known as downwash, channelling coupled with acceleration, and shielding, as illustrated in the image below. Downwash 1 relates to the effect of winds against a tall building, whereby much of the impinging flow on the windward side of the building, nominally below two-thirds of the total height, is directed to lower levels. Taller buildings with smooth façades and no podiums produce the strongest downwash effects at grade, while the presence of protruding balconies and a tower setback from the podium edge mitigates downwash effects at the ground level. Channelling 2 refers to acceleration of wind through gaps between buildings, while acceleration of wind 3 occurs around building corners. Shielding 4 relates to calm zones on the leeward side of buildings, protected from prevailing winds Montreal Road, Ottawa: Qualitative Pedestrian Level Wind Assessment 5

6 3.3. Pedestrian Wind Comfort Guidelines The pedestrian wind comfort guidelines used by GWE, which correspond to industry-accepted standards, are based on the correlation between a variety of pedestrian activity types and acceptable wind speed ranges for those activities. More specifically: Wind conditions are considered to be comfortable for sitting when gust wind speeds less than or equal to 14 kilometers per hour (km/h) occur at least 70% of the time; Wind conditions are considered to be comfortable for standing and strolling when gust wind speeds less than or equal to 22 km/h occur at least 80% of the time; and Wind conditions are considered to be comfortable for walking when gust wind speeds less than or equal to 30 km/h occur at least 80% of the time. The GWE guidelines are based on gust wind speeds, since people are most sensitive to wind gusts rather than to constant wind speeds. The guidelines are applied to the intended use of an outdoor area. For example, an entrance to a building not served by a vestibule or revolving door should be suitable for standing, but need not be suitable for sitting, while a public sidewalk need only be suitable for walking in most circumstances. 4. ANTICIPATED PEDESTRIAN COMFORT Based on consideration of the proposed development Montreal Road, surrounding building massing, and the relationship to the local wind climate, the following statements summarize our opinion of how these influences will affect pedestrian comfort at key areas. Sidewalk Area, Retail Entrances, and Retail Exit along Montreal Road (Tags A, B, and C): The public sidewalk area along the south elevation of the building (Tag A) is exposed to prominent west winds, as well as to east winds that are prominent during the colder months. Wind conditions for the existing site massing are estimated as being suitable for sitting during the summer, standing during the shoulder months of spring and autumn, and suitable for walking during the remaining colder months of the year. Pedestrian wind comfort following the introduction of the proposed development is expected to remain similar to the noted existing conditions, which are considered acceptable for public sidewalks Montreal Road, Ottawa: Qualitative Pedestrian Level Wind Assessment 6

7 Wind conditions tight to the south façade and in the vicinity of the retail entrance and exit (Tag B) will be somewhat calmer than those reported along the sidewalk area. More specifically, the building s cuboid shape with its long axis parallel to Montreal Road will generate a boundary layer that is expected to ensure conditions remain suitable for sitting during the summer, standing during late spring and throughout the autumn months, becoming suitable for walking during the remaining colder months of the year. On this basis, the retail entrance and exit close to the midpoint of the façade are deemed to be acceptable. As a result of occasional strong wind gusts, it is recommended that the retail entrance at the southwest corner of the building (Tag C) either be shifted to the east, away from the building corner, or be served by a vestibule. If it is not feasible to move the entrance, it is suggested that an extension be added to the outer wall at the building corner of no less than 1 m to eliminate the risk of wind gusts pulling the doors open and damaging door hardware. Of particular importance, the moderate windiness of this area will not physically affect pedestrian comfort. Pedestrian Walkway / Surface Parking, and Office Lobby Entrances along West Side of Development (Tag D): The pedestrian walkway / surface parking area leading to the parking garage along the west elevation of the development will be mostly exposed to prominent west winds, resulting in conditions suitable for standing during the summer and autumn seasons, and suitable for walking during the spring and winter seasons, which are considered acceptable. Wind conditions at the entrances providing access to the office lobby will benefit from the building overhand and slight setback into the façade. As a result, the entrances are expected to be suitable and acceptable for sitting during the summer and early autumn months, standing during late spring and the remaining months of autumn, and suitable for walking during the colder winter months. Entrances and Exits serving the Parking Garage (Tags E and F): The entrances and exits serving the parking garage on the west side of the development are well-protected from oncoming winds from the proposed building massing itself, inclusive of the setback of the parking structure from the mixed-use building. Therefore, wind conditions are expected to be suitable for sitting during the summer, becoming suitable for standing, or better, during the remaining months of the year Montreal Road, Ottawa: Qualitative Pedestrian Level Wind Assessment 7

8 The exits leading from the parking garage along the north façade are exposed to prominent west and east winds, which will tend to simultaneously induce pressures (inward-acting) and suctions (outward-acting) on the doors. As a result, wind conditions are expected to be suitable for standing during the summer months, becoming suitable for walking, or better, during the remaining colder months of the year. Although the noted setback of the parking structure will result in increased wind comfort at the exits, it is recommended that the robustness of the door hardware be selected to account for increased wind loading. The moderate windiness of this area will not physically affect pedestrian comfort. Office Terraces on Ninth Level (Tag G): The terraces on the ninth level are located on the four (4) corners of the building. As a result of the sparse massing in close proximity to the subject site, the wind exposures described in Section 2, and the wind directionality and intensity for Ottawa, moderately strong winds are expected to interact with the terraces for the majority of the year. As such, mitigation will be required to ensure conditions suitable for sitting are provided during the typical use period, which is defined as late spring through early autumn. More specifically, given the exposure to west and east winds, we recommend extending the perimeter guards to 1.6 m, measured above the walking surfaces, for all noted terraces. Influence of the Proposed Development on Existing Wind Conditions near the Study Site: In addition to the foregoing, the introduction of the proposed development is not expected to significantly influence pedestrian wind comfort over neighbouring areas at grade. In particular, although modest changes to wind speeds may occur beyond the study site upon introduction of the proposed development, nearby building entrances, sidewalk areas, and other pedestrian areas are generally expected to continue to experience wind conditions similar to those that presently exist without the proposed building in place. Applicability of Predictions: The forgoing statements and conclusions apply to common weather systems, during which no dangerous or consistently strong wind conditions are expected anywhere over the study site. During extreme weather events (i.e., thunderstorms, tornadoes, and downbursts), life safety is the primary concern, which cannot be reliably assessed and is outside the scope of this study. However, these events are generally short-lived and infrequent, and there is often sufficient warning for pedestrians to take appropriate cover. 5. SUMMARY AND RECOMMENDATIONS Montreal Road, Ottawa: Qualitative Pedestrian Level Wind Assessment 8

9 Based on a qualitative analysis of architectural drawings, surrounding building massing, and the wind climate as referenced at Ottawa Macdonald-Cartier International Airport, the following general statements summarize our predictions concerning future wind conditions for the proposed mixed-use office development at Montreal Road, Ottawa. 1. Wind comfort at grade-level pedestrian-sensitive locations across the full study site is expected to be moderate and suitable for the anticipated uses throughout the year. These areas include surrounding public sidewalks, a pedestrian walkway and surface parking area along the west side of the development, and building access points serving the north, west, and south elevations of the subject site. 2. The foregoing assessment (see Section 4) includes suggestions concerning the retail entrance at the southwest corner of the building, as well as the exits on the north side of the parking structure. Implementation of the wind mitigation suggestions will ensure door hardware can adequately contend with the anticipated wind loading. 3. Wind conditions over the corner terraces on the ninth level are expected to be moderately strong throughout the year. As such, mitigation will be required to ensure conditions suitable for sitting are provided during the typical use period, which is defined as late spring through early autumn. More specifically, given the exposure to west and east winds, we recommend extending the perimeter guards to 1.6 m, measured above the walking surfaces, for all noted terraces. 4. The introduction of the proposed building is not expected to significantly influence pedestrian wind comfort at all neighbouring areas beyond the development site. Pedestrian sensitive areas beyond the development site will continue to experience wind conditions similar to those that presently exist without the proposed building in place. The foregoing analysis and statements are based on knowledge and experience of wind flow patterns for the study site and in similar settings. As such, this assessment is intended to ensure adequate pedestrian safety relating to wind, and to provide general guidance relating to pedestrian comfort over the full study site Montreal Road, Ottawa: Qualitative Pedestrian Level Wind Assessment 9

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